Question

the first term of an ap is 5 and the last term is 45 .if the sum of all the terms is 400 the number of terms is​

Answer 1

Answer:

n=16

Step-by-step explanation:

Sn=n/2×a+l

400×2=n(5+45)

800=n(50)

800/50=n

n=16

Answer 2

Answer:

a=5

l=45

Sn=400

Sn=n/2(a+l)

400=n/2(5+45)

400=n/2*50

400/25=n

16=n