Question

Sum $49,44,39,....to17$ terms.

Answer 1

Given series is $49,44,39,......$ to 17 terms

Observe that the given series is in Arithmetic progression with common difference $-5$ and first term as $49$

Sum of first $n$ terms in AP with first term as $a$ and common difference $d$ is $\frac{n}{2}(2a+(n-1\left)d\right)$

Here $a=49$ and $d=-5$

So, the sum of first $17$ terms is $\frac{17}{2}(98-80)=17\times 9=153$