Question

Shown are four number cards.
The mean of the cards is 9.
Work out the missing number.

7 5 8 ?

Answer 1

Step-by-step explanation:

LET NO. BE x

Mean of the no:

$\frac{7 + 8 + 9 + x}{4} = 9 \\ 7 + 8 + 9 + x = 36 \\ 24 + x = 36 \\ x = 36 - 24 \\ x = 12$

HOPE IT HELPS.....