CAT 2018 Number System Question (Hard)

Question

How many two-digit numbers, with a non-zero digit in the units place, are there which are more than thrice the number formed by interchanging the positions of its digits?

Optima Learn · Accepted Answer

Let the two-digit number be 10a b where tens digit 1 to 9 units digit 1 to 9 , since units digit is non-zero Number formed by interchanging digits --- Given Condition 10a b 3 times 10b a Simplify RHS 10a b 30b 3a Bring terms to LHS 10a - 3a 30b - b 7a 29b --- Find integer pairs where Let s compute f

CAT 2018 Number System — Previous Year Question

CAT 2018

Quantitative

Number System

Hard

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