Question

What is the two digit number? i the difference between the two digits is nine ii the sum of the two digits is nine

a. 1 or 2

b. 3

c. 4

d. 5?

Answer 1

So , the 2 digit no . whose sum and difference is nine is ;-

let the ten's digit be      x 
and the once digit be   y

x - y = 9
x + y = 9 

by elimination ;-
2x = 18 
x= 9 

y= 0

so the no. is 90