Question

The first and last terms of an AP are 7 and 49 respectively. If sum of all terms is 420. Find its common difference ?​

Answer 1

Answer:

The first and the last terms of an A.P are 7 and 49, respectively. If the sum of all its terms is 420, find its common difference. ... Hence the common difference of the A.P = 3. Note: [a] This question can also be solved using the formula Sn=n2(2a+(n−1)d).

Answer 2

Answer :-

Given that :-

a = 7

l = 49

Sum = 420

A / q ,

n / 2 ( a + l ) = 420

=> n ( 7 + 49 ) = 420 * 2

=> 56 * n = 420 * 2

=> n * 8 = 60 * 2

=> n * 2 = 15 * 2

=> n = 15 .

Now ,

a + ( n - 1 ) d = 49

=> 7 + ( 15 - 1 ) d = 49

=> 14 d = 42

=> d = 3 .