Question

Out of four number, the average of first three is 16 and that of the last three is 15. If the last number is 18, the
first numbers​

Answer 1

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Given :-

• Out of four number, the average of first three is 16
• Average of last three is 15
• Last number = 18

To find :-

• First number

Solution :-

Let the four numbers be, w, x, y and z.

Average of first three, w, x, y = 16

Total of all three numbers = 16 × 3

Total = 48

Average of last three, x, y, z = 15

Total of all three numbers, = 15 × 3

Total = 45

w + x + y = 48 ---->1

x + y + z = 45 ---->2

Subtract equation 2 from 1

w + x + y - (x + y + z) = 48 - 45

w + x + y - x - y - z = 3

w - z = 3 ----->3

We know the last number is 18, therefore substitute the value in equation 3,

w - 18 = 3

w = 3 + 18

w = 21

•°• First number, w = 21