Question

sum of the first 14 terms of an A.P is 1505 and it's first term is 10 . find its 25th term

Answer 1

Sum of n terms = Sn = n/2 [ 2a + (n-1) d ]
where a = first term, d = common difference

therefore, S14 = 14/2 [2*10 + (14-1) d ] = 1505

solve for d, we get, 215 = 20 + 13d
hence, d = 15.

then ,an = a + (n-1) d
therefore, a25 = 10 + (25-1) 15
a25 = 10 + 24 * 15 = 370.

i hope its help you

Answer 2

HEY Buddy.....!! here is ur answer

Given that : S14 = 1505

As we know that : Sn = n/2[2a+(n–1)d]

where a = 10 and n = 14

According to the question :

1505 = 14/2[2×10+(14–1)d]

=> 1505/7 = 20+13d

=> 215–20 = 13d

=> d = 195/13 = 15

As we know that : nth term = a + (n–1)d

=> 25th term = 10+(25–1)15

=> 25th term = 10+24×15

=> 25th term = 370

I hope it will be helpful for you....!!

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