Question

(iv) For an A.P., the first term is 4 and the last term (t,) is 31. The sum of all the
terms is 420. What is the value of n?
(A) 12 (B) 24 (C) 10 (D) 20



b)24

first term= 4. Last term=31

S(n)=n/2( first term + last term )
420=n/2( 4 + 31 )
420= n/2 (35)
420/35= n/2
12=n/2
12× 2 = n
24 = n
n=24​

Answer 1

Step-by-step explanation:

it is correct explanation:

Answer 2

Given; For an A.P., the first term is 4 and the last term is 31. The sum of all the

terms are 420.

To Find; The value of n

Solution; It is given that For an A.P., the first term is 4 and the last term (t,) is 31. The sum of all the

terms aare20.

The first term, a=4

Last term an= 31

Sum of n terms =420

n(a+an)/2=420

n(35)=840

n=840/3

n=24

Hence the value of n is 24