A certain number of two digits is three times the sum of its digits and if 45 be added to it, the digits are reversed. Then number is	Pick:
A) 21  B) 23  C) 27  D) 72  E) 57
Sol.   Let the ten's digit be x and unit's digit be y.   Then, 10x + y = 3(x+y) ⇒ 7x - 2y = 0   10x + y + 45 = 10y + x ⇒ y - x = 5   Solving (i) and (ii), we get : x = 2 and y = 7.   ∴ Required number = 27.   Answer 27
<result>C</result>
A certain number of two digits is three times the sum of its digits and if 45 be added to it, the digits are reversed. Then number is