The average of three number is 42. The first is twice the

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The average of three number is 42. The first is twice the second and the second is twice the third the different between the third largest and the smallest number number is ?

1. 18
2. 36
3. 54
4. 72

Correct Option: C

Let third number = y
Then, second number = 2y
and first number =4y

⇒ ( y + 2y + 4y) / 3 = 42
⇒ 7y = 42 x 3
⇒ y = 18

so, (largest) - (smallest) = ( 4y - y)
= 3y
=54