How many terms of the AP : 24, 21, 18, ... must be taken so that their sum
is 78?
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Answer:
4 terms and 13 terms
Step-by-step explanation:
a=24,d=-3
so 78=n/2{48+(n-1)×(-3)}
on solving we get
52=16n+n-n^2
n^2-17n+52=0
on factorization we get
(n-13)(n-4)=0
n=13 or 4
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