Question

The digit in tens place of a 2 digit no is 4 times the digit in ones place. If u interchange the digits of this 2 digit no & add the resulting no to the original no, u get 55. Wht is the original no??

(Ans:41)

Answer 1

$let \: the \: unit \: digit \: be \: x \\ then \: ten \: digit = 4x \\ number = 40x + x = 41x \\ according \: to \: question \\ 10x + 4x + 41x = 55 \\ 55x = 55 \\ x = 1 \\ unit \: digit = 1 \: \: and \: ten \: digit = 4 \\ so \: required \: number = 41$