Acertijos

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Toca Respuesta debajo de un acertijo para verla. Intenta cada uno antes de mirar.

1. A bat and a ball cost $1.10 together. The bat costs $1.00 more than the ball. How much does the ball cost?

   Respuesta

   5 cents If the ball costs 5 cents, the bat costs $1.05. Together they cost $1.10, and the bat costs $1.00 more.

2. A patch of lily pads doubles in size every day. It covers the whole pond on day 48. On which day does it cover half the pond?

   Respuesta

   Day 47 The patch doubles each day, so one day before it covers the whole pond, it covers half.

3. 5 machines make 5 toys in 5 minutes. How long do 100 machines take to make 100 toys?

   Respuesta

   5 minutes Each machine makes one toy in 5 minutes. 100 machines work at the same time, so they make 100 toys in 5 minutes.

4. A clock takes 5 seconds to strike 6 o'clock. How long does it take to strike 12 o'clock?

   Respuesta

   11 seconds 6 strikes have 5 gaps, so each gap is 1 second. 12 strikes have 11 gaps: 11 seconds.

5. How many 2-cent stamps are there in a dozen?

   Respuesta

   12 A dozen is always 12, whatever the stamps cost.

6. A snail is at the bottom of a well 10 meters deep. Each day it climbs 3 meters, and each night it slides back 2 meters. On which day does it reach the top?

   Respuesta

   Day 8 After 7 days and nights it is 7 meters up. On day 8 it climbs 3 meters and reaches 10 meters before night.

7. A drawer holds 10 black socks and 10 white socks. In the dark, how many socks must you take out to be sure you have a pair that matches?

   Respuesta

   3 Two socks can be one of each color. The third sock always matches one of them.

8. 3 cats catch 3 mice in 3 minutes. How many cats does it take to catch 100 mice in 100 minutes?

   Respuesta

   3 Together the 3 cats catch one mouse a minute, so in 100 minutes they catch 100 mice.

9. Ana is twice as old as Ben. In 10 years, Ana will be one and a half times as old as Ben. How old is Ben now?

   Respuesta

   10 Ben is 10 and Ana is 20. In 10 years Ben is 20 and Ana is 30, which is one and a half times 20.

10. What do you get when you add all the whole numbers from 1 to 100?

    Respuesta

    5050 1 + 100, 2 + 99, 3 + 98 and so on make 50 pairs of 101. 50 times 101 is 5,050.

11. Six friends meet, and each friend shakes hands once with each of the others. How many handshakes are there?

    Respuesta

    15 6 friends times 5 handshakes is 30, and each handshake is counted twice: 15.

12. What is half of 2 plus 2?

    Respuesta

    3 Half of 2 is 1, and 1 plus 2 is 3.

13. Use eight 8s and only addition to make 1,000.

    Respuesta

    888 + 88 + 8 + 8 + 8 888 + 88 + 8 + 8 + 8 = 1,000, with eight 8s in all.

14. The pages of a book are numbered from 1. The numbers use 192 digits in all. How many pages does the book have?

    Respuesta

    100 Pages 1 to 99 use 189 digits. The 3 digits left make page 100.

15. You drive to a town 60 km away at 30 km an hour. How fast must you drive back to average 60 km an hour for the whole trip?

    Respuesta

    It is not possible 120 km at 60 km an hour takes 2 hours. The trip there already took 2 hours, so no speed is fast enough.

16. What is the smallest number that leaves a remainder of 1 when you divide it by 2, 3, 4, 5, or 6?

    Respuesta

    61 60 is the smallest number that 2, 3, 4, 5 and 6 all divide. 60 + 1 = 61.

17. Which number comes next: 2, 6, 12, 20, 30, ?

    Respuesta

    42 The gaps grow by 2 each time, so the next gap is 12. 30 + 12 = 42.

18. What comes next: 1, 11, 21, 1211, 111221, ?

    Respuesta

    312211 Each line describes the one before: 111221 is three 1s, two 2s and one 1, so 312211.

19. A hen and a half lay an egg and a half in a day and a half. How many eggs does one hen lay in 3 days?

    Respuesta

    2 One hen lays one egg in a day and a half, so in 3 days it lays 2 eggs.

20. A brick weighs 1 kg plus half a brick. How much does the whole brick weigh?

    Respuesta

    2 kg Half a brick weighs 1 kg, so the whole brick weighs 2 kg.

21. Divide 30 by a half, then add 10. What do you get?

    Respuesta

    70 30 divided by a half is 60, because 60 halves make 30. 60 + 10 = 70.

22. How many times does the digit 7 appear in the numbers from 1 to 100?

    Respuesta

    20 7, 17, 27 and so on give 10 sevens in the ones place. 70 to 79 give 10 more in the tens place.

23. Mia has 4 sisters, and each of the sisters has 1 brother. How many children are in the family?

    Respuesta

    6 5 girls, Mia and her 4 sisters, share 1 brother: 6 children.

24. A girl has as many brothers as sisters, but each of her brothers has half as many brothers as sisters. How many children are in the family?

    Respuesta

    7 4 girls and 3 boys. Each girl has 3 sisters and 3 brothers. Each boy has 2 brothers and 4 sisters.

25. It takes 10 minutes to boil one egg. How long does it take to boil 4 eggs in the same pot?

    Respuesta

    10 minutes The eggs boil together, so 4 eggs take 10 minutes, the same as one.

26. A train 1 km long goes through a tunnel 1 km long at 1 km a minute. How long until the whole train is out of the tunnel?

    Respuesta

    2 minutes The front goes 1 km through the tunnel, then 1 km more until the back is out: 2 km at 1 km a minute.

27. A shirt costs $100. The price goes down by 50%, then up by 50%. What does the shirt cost now?

    Respuesta

    $75 Half of $100 is $50. 50% of $50 is $25, so the price goes up to $75.

28. Multiply all ten digits of a phone keypad together. What do you get?

    Respuesta

    0 One of the keys is 0, and any number times 0 is 0.

29. How many squares of any size are there on a chessboard?

    Respuesta

    204 64 + 49 + 36 + 25 + 16 + 9 + 4 + 1 = 204.

30. Three boxes say Apples, Oranges, and Mixed. Every label is wrong. You may take one fruit out of one box without looking. Which box do you pick from to fix all the labels?

    Respuesta

    The box labeled Mixed The Mixed box holds only one kind. If you draw an apple, it is the apple box, and the other two labels follow.

31. Three switches downstairs work one lamp upstairs. You may go upstairs only once. How do you find the right switch?

    Respuesta

    Feel the bulb for heat Turn switch 1 on for a few minutes, turn it off, and turn switch 2 on. Upstairs: on is 2, warm is 1, cold is 3.

32. Leo points at a photo and says: I have no brothers or sisters, but this man's father is my father's son. Who is in the photo?

    Respuesta

    Leo's son Leo's father's only son is Leo. So the man's father is Leo, and the man is Leo's son.

33. Two US coins add up to 30 cents, and one of them is not a nickel. Which coins are they?

    Respuesta

    A quarter and a nickel A quarter and a nickel. The quarter is the one that is not a nickel.

34. In a race, you pass the runner in last place. Which place are you in now?

    Respuesta

    That is not possible Nobody is behind the last runner, so you cannot pass them.

35. A farmer must cross a river with a fox, a hen, and a bag of corn. The boat holds the farmer and one more. Left alone, the fox chases the hen, and the hen pecks the corn. What does the farmer take across first?

    Respuesta

    The hen Take the hen first. Then bring the fox over and the hen back, take the corn over, and fetch the hen last.

36. On an island, some people always tell the truth, and the rest always lie. Ana says: Ben and I are both liars. Who tells the truth?

    Respuesta

    Ben If Ana told the truth, she would be a liar. So Ana lies, and her words are false: Ben must tell the truth.

37. The tomorrow of yesterday was Wednesday. What day is it today?

    Respuesta

    Wednesday The day after yesterday is today, so today is Wednesday.

38. The day after tomorrow is a Sunday. What day was yesterday?

    Respuesta

    Thursday If the day after tomorrow is Sunday, today is Friday, so yesterday was Thursday.

39. In a race, Ava finished after Cal but before Ben. Dev finished after Ben. Who won?

    Respuesta

    Cal The order is Cal, Ava, Ben, Dev. Cal won.

40. What letter comes next: J, F, M, A, M, J, J, A, S, O, N, ?

    Respuesta

    D They are the first letters of the months, and December comes after November.

41. Is it right to say the yolk of the egg is white, or the yolk of the egg are white?

    Respuesta

    Neither, the yolk is yellow Neither. An egg yolk is yellow.

42. You walk into a dark room with one match. There is a candle, an oil lamp, and a fireplace. What do you light first?

    Respuesta

    The match You must light the match before you can light anything else.

43. A man walked in the rain for an hour with no umbrella and no hat, but not one hair on his head got wet. How?

    Respuesta

    He is bald He has no hair on his head.

44. A man pushes his car to a hotel and tells the owner that he is out of money. Why?

    Respuesta

    He is playing Monopoly He is playing a board game. His piece is a car, and he landed on a square with a hotel.

45. How can a person go eight days without sleep?

    Respuesta

    They sleep at night They sleep every night, so they never need to sleep in the day.

46. A boy falls off a 20-foot ladder but is not hurt at all. How?

    Respuesta

    He fell off the bottom step He was on the lowest step, close to the ground.

47. A truck driver goes the wrong way down a one-way street, and the police watch but do nothing. Why?

    Respuesta

    He was walking He is on foot. A person may walk either way on a one-way street.

48. Two people play five games of checkers. Each one wins the same number of games, and no game is a tie. How?

    Respuesta

    They played other people They did not play each other. Each of them played someone else.

49. In a one-story house, everything is yellow: the walls, the doors, the lamps. What color are the stairs?

    Respuesta

    There are no stairs A one-story house has no stairs.

50. A red house is made of red bricks, and a blue house is made of blue bricks. What is a greenhouse made of?

    Respuesta

    Glass A greenhouse is a house of glass where plants grow.

51. A man lives on the 10th floor. He takes the lift down every day. Coming home, he rides only to the 7th floor and walks up, except on rainy days. Why?

    Respuesta

    He is too short to reach the button He is short and can reach only the 7th floor button. On rainy days, he presses 10 with his umbrella.

52. Which five-letter word reads the same when you turn it upside down?

    Respuesta

    SWIMS Write SWIMS in capitals and turn the page around: it still reads SWIMS.

53. Name a nine-letter word that stays a word each time you take away one letter, all the way down to one letter.

    Respuesta

    Startling Startling, starling, staring, string, sting, sing, sin, in, I.

54. Move the letters of NEW DOOR to make one word.

    Respuesta

    One word The letters of NEW DOOR spell ONE WORD.

55. Move the letters of LISTEN to make a word that means quiet.

    Respuesta

    Silent LISTEN and SILENT use the same six letters.

56. Which one does not belong: apple, banana, carrot, grape?

    Respuesta

    Carrot A carrot is a vegetable. The others are fruits.

57. Which number does not belong: 2, 3, 5, 9, 11?

    Respuesta

    9 9 is 3 times 3. The others are prime numbers.

58. Name a common English word that has two letter Us next to each other.

    Respuesta

    Vacuum Vacuum has two Us in a row.

59. Which word starts with IS, ends with AND, and has LA in the middle?

    Respuesta

    Island IS + LA + AND spells ISLAND.

60. Say silk three times, fast. Now: what do cows drink?

    Respuesta

    Water Cows drink water. Milk is what they make.

61. How many birthdays does the average person have?

    Respuesta

    One Each person is born once. The other days are anniversaries of that birthday.

62. You have 6 apples in one hand and 7 apples in the other. What do you have?

    Respuesta

    Very big hands You would need very big hands to hold 13 apples.

63. Two girls are born to the same mother, on the same day, in the same year. They are not twins. How?

    Respuesta

    They are triplets They are two of a set of triplets.

64. Which side of a cat has the most fur?

    Respuesta

    The outside The outside of a cat has all of its fur.

65. How can you drop a raw egg onto a concrete floor without cracking the floor?

    Respuesta

    Any way you like An egg cannot crack a concrete floor, so any drop works.

66. You throw a white stone into the Red Sea. What does it become?

    Respuesta

    Wet It becomes wet.

67. Which is bigger: 2 to the power of 10, or 10 to the power of 3?

    Respuesta

    2 to the power of 10 2 to the power of 10 is 1,024. 10 to the power of 3 is 1,000.

68. What is 25% of 80, plus 80% of 25?

    Respuesta

    40 25% of 80 is 20, and 80% of 25 is 20. 20 + 20 = 40.

69. Draw a triangle, then draw one line from a corner to the opposite side. How many triangles are there now?

    Respuesta

    3 There are 2 small triangles and the big one: 3.

70. Think of a number. Multiply it by 3, add 6, divide by 3, and take away the number you started with. What do you get?

    Respuesta

    2 Times 3, then divide by 3, gives the number back plus 2. Take the number away, and 2 is left.

71. A rope ladder hangs over the side of a ship, with its lowest rung just above the water. The tide rises by 1 meter. How many rungs are under water now?

    Respuesta

    None The ship floats, so it rises with the water, and so does the ladder.

72. Which is right: 7 + 8 = 13, or 7 + 8 = 14?

    Respuesta

    Neither Neither. 7 + 8 = 15.

73. How much dirt is there in a hole 2 meters deep and 1 meter wide?

    Respuesta

    None A hole is empty: there is no dirt in it.

74. Which number comes next: 3, 6, 11, 18, 27, ?

    Respuesta

    38 The gaps are the odd numbers, so the next gap is 11. 27 + 11 = 38.

75. Fill the gap: 2, 4, 8, 16, __, 64. Which number goes there?

    Respuesta

    32 16 doubled is 32, and 32 doubled is 64.

76. Move the letters of CIFAIPC. Do you get a city, an animal, an ocean, or a river?

    Respuesta

    An ocean The letters spell PACIFIC, the Pacific Ocean.

77. You face north. You turn right, then right again, then left. Which way do you face now?

    Respuesta

    East Right turns you to east, then south. Left from south turns you to east.

78. You write every number from 1 to 50. How many times do you write the digit 1?

    Respuesta

    15 1, 11, 21, 31 and 41 give 5 ones in the ones place. 10 to 19 give 10 more in the tens place.

79. Liam is taller than Zoe. Zoe is taller than Max. Is Max taller than Liam?

    Respuesta

    No Liam is taller than Zoe, and Zoe is taller than Max, so Liam is taller than Max.

80. All bloops are razzies. All razzies are lazzies. Are all bloops lazzies?

    Respuesta

    Yes Every bloop is a razzie, and every razzie is a lazzie, so every bloop is a lazzie.

81. An explorer walks 1 km south, 1 km east, and 1 km north, and ends where she started. She sees a bear. What color is the bear?

    Respuesta

    White She started at the North Pole, so the bear is a polar bear: white.

82. How many months of the year have 31 days?

    Respuesta

    7 January, March, May, July, August, October and December have 31 days.

83. With 3 straight cuts in any direction, what is the most pieces you can cut a round cake into?

    Respuesta

    8 Two cuts from above make 4 pieces. A third cut sideways through the middle halves each one: 8.

84. Which number comes next: 1, 2, 4, 7, 11, ?

    Respuesta

    16 The next gap is 5. 11 + 5 = 16.

85. A store sells 3 apples for 60 cents. How much do 7 apples cost?

    Respuesta

    $1.40 One apple costs 20 cents, so 7 apples cost 140 cents, or $1.40.

86. If you have only one, you want to share it. If you share it, you do not have it anymore. What is it?

    Respuesta

    A secret A secret stops being a secret once you share it.

87. Some months have 30 days, and some have 31. How many months have 30 days or more?

    Respuesta

    11 Every month but February has 30 days or more.