Question

The average of three numbers is 21.if the first number is double of the second number and the second number is double of the third number, find the first number

Answer 1

x+2x+4x=21.3
7x=21.3
x=3.3
x=9

Answer 2

Let the third number be x.
Therefore the second number will be 3x.
Therefore the first number will be 3x × 2 that is six 6x.
Average =sum of all values ÷number of values
number of values=3 and sum of values is x + 3x+ 6x = 11x.

Average=21
so, therefore
21 = 11x÷3
21×3=11x
63=11x.
63÷11=x
x=5.72

so, third number is 5.72
second number =3x= 17.16
third number=6x= 34.32

I hope this will help.
please mark this as brainliest answer.