Question

If the sum of 'n' terms of A.P 2, 5, 8,
is 155, then the number of terms is
O 1) 11
O2) 10
O 3) 9
O4) 12​

Answer 1

Answer:

the number of term is O2) 10

Answer 2

Given

sum of n terms of AP 2,5,8 is 155

To Find

we have to find the number of terms

$\sf\huge {\underline{\underline{{Solution}}}}$

AP : 2,5,8 ..

here ,first term (a) is 2

second term (a2) = 5

common difference (d) = a2-a1

d= 5-2= 3

Now, using formula

an= a+(n-1)d

(an= nth term )

an= 155

a= 2

d= 3

155= 2+(n-1)3

155=2+3n-3

155= 3n-1

3n= 156

n= 156/3= 52

Hence, number of term is 52

Extra information=>

If n term is given and to find sum we use :

• Sum (sn)= n/2[2a+(n-1)d

if last term is given and to find sum we use :

• Sum(sn) = n/2( a+l)