Question
Fri February 13, 2009 By:

alogorithm

Expert Reply
Sat February 14, 2009

Assum that the first term of the A.P. is a and the common difference is d,

Then the nth term is given by the formula

nth term= a+(n-1)d

Acording to the question,

required expression =[a+(n-1)d]-[a+(k-1)d]=(n-k)d

when the 20th term is 10 more than the 18 th term,

(a+19d)=10+(a+17d)

So,

2d=10

d=5

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