Question

Find two numbers such that one of them exceeds the other by 9 and their sum is 81.

Answer 1

Let the no`s be x and y 
Then x - y = 9 ---------- eq(1)   [given as a no exceeds the other by 9]
Also x + y = 81 eq(2)
Add eq (1) and (2)
x - y = 9
x + y = 81
2x     = 90
x = 90/2
∴x = 45
Substituting x in eq 2
x + y = 81
⇒45 + y = 81
⇒y = 81 - 45
∴ y = 36
∴The no`s are 45 and 36

Answer 2

x+x+9=81
=>2x+9=81
=>2x=81-9
=>2x=72
=>x=72/2
=>x=36
: no.=36 and another no.= 36+9=45