Question

Which expression defines the given series for seven terms?

8 + 13 + 18 + . . .

Answer 1

The given question is 8+13+18+...... which is in arithmetic progression . And for arithmetic series, we have to use the following formula for nth term .

$a_{n} = a + (n-1)d$

Here a =8 , d=5

So we get

$a_{n} = 8+(n-1)5 = 5n +3$

And the required expression for n=7 is

$\sum_{n=1}^{7}(5n+3)$