Question

Out of four numbers, the average of the first three numbers is thrice the fourth number. if the average of the four numbers is 5, the fourth number is : (a) 4.5 (b) 5 (c) 2 (d) 4

Answer 1

let the no. a,b,c,d
(a+b+c)/3=3d
a+b+c=9d
according to data a+b+c+d=5*4=20
then. 9d+d=20
10d=20
d=20/10=2

Answer 2

Answer:

2

Step-by-step explanation:

Let the four no. be a,b,c,d

We are given that  the average of the first three numbers is thrice the fourth number.

So, $\frac{a+b+c}{3}=3d$

$a+b+c=9d$ --A

We are given that the average of the four numbers is 5

So, $\frac{a+b+c+d}{4}=5$

$a+b+c+d=5 \times 4 = 20$

Using A

$9d+d= 20$

$10d= 20$

d=2

Hence the fourth number is 2