Question

Find the sum upto 20 terms of the series 20+ 35+ 50+...

Answer 1

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Answer 2

SOLUTION

TO DETERMINE

The sum upto 20 terms of the series

20 + 35 + 50 + ...

EVALUATION

Here the given series is

20 + 35 + 50 + ...

This is an arithmetic progression

First term = a = 20

Common Difference = d = 35 - 20 = 15

Number of terms = n = 20

Hence the required sum

$\displaystyle \sf{ = \frac{n}{2} \bigg[ 2a + (n - 1)d\bigg] }$

$\displaystyle \sf{ = \frac{20}{2} \bigg[ 2 \times 20 + (20 - 1) \times 15\bigg] }$

$\displaystyle \sf{ =10 \bigg[ 40 + 285\bigg] }$

$\displaystyle \sf{ =10 \times 325 }$

$\displaystyle \sf{ =3250 }$

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