Question

Find the sum of the first 40 positive integers

Answer 1

Solution :

The first positive integers divisible by 6 are 6, 12, 18, .... Clearly, it is an AP with first term a = 6 and common difference d = 6. We want to find $S_{40}$.

∴ $S_{40}$ = $\frac{40}{2}$ [2 × 6 + (40 - 1) 6]

                             = 20(12 + 39 × 6)

                             = 20(12 + 234) = 20 × 246 = 4920

Answer 2

Step-by-step explanation:

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