Question

A two digit number is such that the product of its digits is 20.If 9 is added to the number the digits interchange thierry places.Dind the number

Answer 1

let the unit place of a number be y and ten's place be X
given number is 10x+y
a/q
XY= 20
X= 20/y. (1)
and 10x+ Y +9 = 10Y+ X
9y-9x = 9
y-x = 1
y - 20/y = 1
y² - y -20 = 0
after solving we get
y = 5and X=4
required no. is 45