CAT 2021

Slot 1

QA

Question & Solution

Let the numbers be of the form 100a+10b+c, where a, b, and c represent single digits.

Then (100c+10b+a)-(100a+10b+c)=198

$99c - 99a = 198$

$c-a = 2$

Now, a can take the values 1-7. a cannot be zero as the initial number has 3 digits and cannot be 8 or 9 as then c would not be a single-digit number.

Thus, there can be 7 cases.

B can take the value of any digit from 0-9, as it does not affect the answer.

Hence, the total cases will be $7\times\ 10=70$.