Question

if the mean of 3, 5, 7, 9 X is 5 find the value of x

Answer 1

$mean = \frac{sum \: of \: all \: numbers}{total \: count \: of \: numbers} \\ \\ mean = \frac{3 + 5 + 7 + 9 + x}{5} \\ \\ 5 = \frac{24 + x}{5} \\ \\ 5 \times 5 = 24 + x \\ \\ 25 = 24 + x \\ \\ 25 - 24 = x$
Ans. X = 1

Answer 2

mean= sum of observation ÷no of observation

so 5=3+5+7+9+X÷5
so...5=24+X÷5
and 25= 24+X
X= 1
Hope it may help you