Question

Out of 4 numbers,thr average of first three number is thrice the fourth number . If the average of the four number is 5, the fourth number is.

Answer 1

Step-by-step explanation:

Average of four number is 5.

a+b+c+d/4=5

a+b+c+d=20

a+b+c=20-d

Average of three number=a+b+c/3

=20-d/3

but average of a+b+c=3*d

Therefore

20-d/3=3*d

20-d=9d

20=10d

d=2

hence the fourth number us 2