Question

The mean of 4 numbers is 12.The mean of 3 is 14.What is the value of the 4th number

Answer 1

The mean of 4 numbers is 12

$${a_1+a_2+a_3+a_4\over 4}=12$$

$$a_4=12(4)-(a_1+a_2+a_3)$$

The mean of 3 numbers is 14

$${a_1+a_2+a_3\over 3}=14$$

$$a_1+ a_2+a_3=14(3)$$

Then

$$a_4=48-42=6$$

 The value of the 4th number is $6.$