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CAT 1997 — QA Question 15

RatioEasy
Passage / Data

Answer the next 3 questions based on the following information.

There are 60 students in a class. These students are divided into three groups A, B and C of 15, 20 and 25 students each. The groups A and C are combined to form group D.

A student instead of finding the value of 78 of a number, found the value of 718 of the number. If his answer differed from the actual one by 770, find the number.

Answer & solution

  • 1584

  • B

    2520

  • C

    1728

  • D

    1656

Solution

This equation is very straightforward. If the number is 'x', then 7x8-7x18=770. On solving this equation, we get x = 1584. Hint: Students please note that if the difference in 78 and 718 of a number is 770, then the difference in 18 and 118 of the number should be 110. If we express this as an equation, we get  x8-x18=110

or 10x = 110 × 18 × 8
or x = 11 × 18 × 8
You can further proceed from here in two ways: (i) the last digit of the required answer should be (1 × 8 × 8) = 4, (ii) number should be divisible by 11. In both cases, the answer that is obtained from the given choices is 1584.

CAT 1997 QA Q15: A student instead of finding the value of 7 8 of a number, found the value of 7 18 of the number. If his answe — Solution | TheCATExam