Question

which term of AP 3,10,17...., will be 84 more than its 13th term

Answer 1

a = 3

d = 7 ,

13th term will be ,

xa13 = a + 12d

a13 = 3 + 12×7

a13 = 3+ 84 = 87

Since , 84 more than its 13th term ,so ,

value of term will be = 87 + 84 = 171

So value of term is 171

Now using ,

an = a+(n-1)d

171 = 3 + 7n - 7

171 + 4 = 7n

175/7 = n

n = 25 ,

So 25th term will be 84 more than its 13th term ,

Verification :-

a25 = a + 24 d

a25 = 3 + 24×7

a25 = 3 + 168 = 171

Answer 2

a = 3…………
d= 7……………
 a13 = a + 12ddd.......,.……...
 = 3 + 84……….…
 = 87................
 hence, 87+ 84………….
 = 171……….
an= 3 + 7n -7…….…
171 = 7n - 4…........
7n = 175..............
n = 25.