Question

In an A.P the 1st term is 20  and the last term is 200.and their are 18 terms . Find the sum of the terms​

Answer 1

Answer:

We know, in AP, where a is the first term and l is the term, and number of terms is n.

Sum of n terms is given by -

S = $\dfrac{n}{2} \{ 2a + (n-1)d\}$,

d is the common difference

S = $\dfrac{n}{2} \{ a + l\}$

Here, we are not given with the common difference (d), so we will apply the 2nd formula-

a = 20

l = 200

n = 18

Hence,

Sum of terms -

= > $\dfrac{18}{2} \{ 20 + 200 \}$

= > 9( 220 )

= > 1980

Sum of first 18 terms is 1980