How many terms of the A.P 25, 22, 19............... must be taken to give a sum of 116? Also find the last term
Answers
Answered by
56
use formula
Sn=n/2 {2a+(n-1) d}
where a is first term and d is common difference.
116=n/2 {2 x 25+ (n-1)(-3)}
232=n (50-3n+3)
232=53n-3n^2
3n^2-53n+232=0
use quadratic formula
n=8,58/6
but n=58/6 isn't possible
hence n=8
last term
t8=a+7d=25-21=4
Sn=n/2 {2a+(n-1) d}
where a is first term and d is common difference.
116=n/2 {2 x 25+ (n-1)(-3)}
232=n (50-3n+3)
232=53n-3n^2
3n^2-53n+232=0
use quadratic formula
n=8,58/6
but n=58/6 isn't possible
hence n=8
last term
t8=a+7d=25-21=4
Answered by
11
last term of series is 4.
number of terms is 8
.
number of terms is 8
.
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