Question 65

The average of the first four numbers is three times the fifth number. If the average of all the five numbers is 85.8, then the fifth number is:

Solution

Let the fifth number be x.

The average of the first four numbers = 3x

Sum of all the first four numbers = 3x $$\times 4$$ = 12x

The average of all the five numbers = 85.8

Sum of all the five numbers = 85.8 $$\times$$ 5 = 429

Sum of all the first four numbers + 5th number = 429

12x + x = 429

x = 429/13 = 33

$$\therefore$$ The 5th number is 33.

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