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Brain teaser

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  • If 7 cIts kill 7 rats in 7 minutes.How many would be needed to kill one hundred rats in 50 minutes?
    7 Cat ----- 7 Rats 1 rat ---- 7 mins 100 rat ---- 7 x 100 = 700 mins 700/50 = 14 Cats
  • What can you between 7 and 8 so that the result is greater than 7 and less than 8?
    7.8
  • I am an odd number. Take away one letter and I become even. What number am I?
    Seven
  • Sally is 54 years old and her mother is 80, how many years ago was Sally’s mother times her age?
    41 years ago
  • The numbers x , y , z and w have an average equal to 25. The average of x , y and z is equal to 27. Find w.
    w = 19
  • A rectangle field has an area of 300 square meters and a perimeter of 80 meters. What are the length and width of the field?
    length L = 30 meters and a width W = 10 meters
  • How to get a number 100 by using four sevens (7’s) and a one (1)?
    Answer 1: 177 – 77 = 100 ; Answer 2: (7+7) * (7 + (1/7)) = 100
  • In a race, the man who came 16 places in front of the last man finished 3 places ahead of the man who came 7th. How many contestants were there?
    1 to 20 constant
  • There is a three-digit number. The second digit is four times as big as the third digit, while the first digit is three less than the second digit. What is the number?
    141
  • A fraction has the denominator greater than its numerator by 6. But you add 8 to the denominator, the value of the fraction would then become 1/3. Can you find this fraction?
    7/13
  • A car travels from A to B at a speed of 40 mph then returns, using the same road, from B to A at a speed of 60 mph. What is the average speed for the round trip?
    T = x / 40 + x / 60 = 100 x / 2400 = x / 24 The average speed is given by 2x / (x/24) = 48 mph