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NCHMCT JEE 2024 Solved Paper

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Question : 21 of 200

Marks: +1, -0

What is the average of first 16 multiples of 9 ?

72
76.5
77.25
79.75

Solution:

Concept:

Average of first

n

multiples of a number = number

\times \frac{n+1}{2}

.

Explanation:

First 16 multiples of 9 are

9, 18, 27, \dots, 144

.

Their sum is

9(1 + 2 + 3 + \dots + 16)

.

Sum of first 16 natural numbers is

\frac{16 \times 17}{2} = 136

.

So, total sum

= 9 \times 136 = 1224

.

Average

= \frac{1224}{16} = 76.5

.

Answer:

B. 76.5

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