Question

Q25. The first and the last terms of an AP are 7 and 49 respectively. If the sum of all terms is
420, find the number of terms in this AP.​

Answer 1

Answer:

answer 108

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Answer 2

Answer:

3

Step-by-step explanation:

a=7 l=49 Sn=420

Sn=

2

n

[a+l]

So 420×2=n[7+49]

n=15

l=a+(n−1)d

⇒ 49=7+14 d

⇒ 7=1+2 d ⇒ 2d=6

⇒ d=3