Question

15. The average of 8 numbers is 20. The average of first two numbers is 151/2
and that of the next three is 211/3. If the sixth number be less than the
seventh and eighth numbers by 4 and 7 respectively, then the eighth number
is.​

Answer 1

Answer:

25

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Step-by-step explanation:

Let the eighth no. be  x

then the seventh = x + 4 and the eighth = x + 7

According to the question,

2×312+3×643+x+x+4+x+7=8×20

31 + 64 + 3x + 11 = 160

106 + 3x = 160

3x = 54

x = 18

∴ Eighth no. x + 7 = 18 + 7 = 25