Question

sum of first 20 terms of an A.P is -240and its first term is 7. find its 24th term

Answer 1

I hope ..... this is correct answer

Answer 2

Answer:

-39

Step-by-step explanation:

Formula of first n terms =$\frac{n}{2}(2a+(n-1)d)$

First term = a = 7

Sum of first 20 terms =$\frac{20}{2}(2(7)+(20-1)d)$

Now we are also given that sum of first 20 terms of an A.P is -240

So, $-240=\frac{20}{2}(2(7)+(20-1)d)$

$-24=(14+19d)$

$-38=19d$

$-2=d$

So, common difference = d = -2

Formula of nth term = $a_n=a+(n-1)d$

Substitute n = 24

$a_{24}=7+(24-1)(-2)$

$a_{24}=-39$

Hence 24th term is -39