Question

first term of ap is 5. last term is 45. sum is 400. find number of terms and common difference​

Answer 1

Answer:

Hope this helps u : )

Let the no. of terms be n

Let the first term be a

We know , in an A.P.

where the first term (a) and last term (l) is known ,

                  sum of n terms = n/2(a+l)

∴ 400 = n/2(5+45)

  ⇒  n = (400*2)/50

  ⇒  n = 16

∴ There are 16 terms in the A.P.

Answer 2

a=5

l=45

Sn=400

then,by using the formula

Sn=n/2{a+l}

400=n/2{5+45}

400=n/2×50

400=25n

n=400/25

n=16

for common difference,

l=a+(n-1)d

45=5+(16-1)d

45-5=15d

or,15d=40

d=40/15

d=8/3 ( dividing by 5)