Q1 of 167 Page 20

Mark the correct alternative in the following:

If 7th and 13th terms of an A.P. be 34 and 64 respectively, then its 18th term is


Here,a7=34 and a13=64


i.e. a+6d=34____(i) and a+12d=64_____(ii)


Subtracting (i) from (ii) we get,


(12-6)d=64-34


∴6d=30


∴ d=5


Substituting d=5 in (i) we get,


a+6(5)=34


∴a+30=34


∴ a=4


Now,18th term is given by a18=a+17d


=4+17×5


=89

More from this chapter

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10

If mth term of an A.P. is n and nth term is m, then write its pth term.

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If the sum of n terms of two A.P.’s are in the ratio (3n + 2) : (2n + 3), find the ratio of their 12th terms.

 2

Mark the correct alternative in the following:

If the sum of p terms of an A.P. is q and the sum of q terms is p, then the sum or p + q terms will be


 3

Mark the correct alternative in the following:

If the sum of n terms of an A.P. be 3 and its common difference is 6, then its first term is