Question

If 12th term of an AP is 25 and 3 points
sum of its first four terms is
24. Then find sum of its first 10
terms."
O 120
O 21
O 100
O None of these​

Answer 1

Answer:

10th

Maths

Arithmetic Progressions

General Formula for nth Term

Second and fourth term of o...

MATHS

Second and fourth term of on A.P. is 12 and 20 respectively. Find the sum of first 25 terms of the A.P.

MEDIUM

Share

Study later

ANSWER

Let a and d be the first term and the common difference of the given AP respectively. Then,

a

2

=12⇒a+d=12 ...(1)

a

4

=20⇒a+3d=20 ...(2)

On subtracting (1) from (2), we get

2d=8⇒d=4

Putting d=4in (1), we get

a=12−4=8

Now, S

25

=

2

25

[2×8+(25−1)×4]=25×56=1400

Hence, Required sum=1400.