Ask a New Question

if the third term of an A.P is 9and its tenth termis 21, thenthe sum if its first 12th terms is...

1 answer

third term of an A.P is 9 ---> a+2d = 9
tenth term is 21 ---> a+9d = 21
subtract them:
7d = 12
d = 12/7

in a+2d=9
a+ 24/7 = 9
a = 39/7

sum(12) = (12/2)( 78/7 + 11(12/7)) = 180

Ask a New Question or answer this question.

Similar Questions

The 3rd term of an A.p is more than the first term, while the fifth termis 15 more than the second term.find the sum of the 8
1. 1 answer
The fifth term of a Gp is 18 morethan the second term. If the difference between the seventh and the fourth term is 162. Find
1. 3 answers
1.The tenth term of an arithmetic progression is68 and the common difference is 7 find the term2.the second term of an
1. 1 answer
The sum of sixth term of a.p is 72 and the second term is seven times fifth term find the first term,common difference and the
1. 3 answers

more similar questions