Question

the first term of an ap is5 and last term is 45.if the sum of all the terms is 400, the number of terms is
A 20
B 8
C 10
D 16​

Answer 1

Answer:

16

Step-by-step explanation:

first term a=5, last term l=45 and Sn = 400

Since, Sn=2n(a+l)

⇒400=2n(5+45)

⇒400=2n(50)

⇒400=n(25)

⇒n=16