When you reverse the digits of the number 13, the number increases by 18. How many other two-digit numbers increase by 18 when their digits are reversed?

A 5
B 6
C 7
D 8

Correct Answer: 6

Let 10x + y be a two digit number, where x and y are positive single digit integers and x>0.Its reverse = 10y + xNow, 10y + x - 10x - y = 18∴ 9(y - x) = 18 ∴ y - x = 2Thus y and x can be (1, 3), (2, 4), (3, 5), (4, 6), (5, 7), (6, 8) and (7, 9)∴ Other than 13, there are 6 such numbers.
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