How many terms of the A.P. 55, 51, 47, ............. must be taken 50 that their sum is 405
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Answer:
Step-by-step explanation:
sum of n terms in ap= n/2(a+l)
where l=a+(n-1)d
405= n/2( 2*55-4(n-1))
by solving we get
2n^2-57n+405=0
2n^2-27n-30n+405=0
n=27/2 or n=15
number of terms cannot be a fraction so n=15
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