Question

The average of 15 and x is 9

Answer 1

$\boxed{\bold{Average \:of \:a \:and \:b =\frac{a+b}{2}}}$

Given,

• Average = 9
• a = 15
• b = x

$\bold{9=\frac{15+x}{2}}$

$\implies\bold{15+x=18}$

$\implies\bold{x=18-15}$

$\implies\bold{x=3}$

$\boxed{\bold{\therefore{x=3}}}}$

Answer 2

15+x/2=9
9x2=15+x
18=15+x
18-15=x
3=x