Question

How many terms of an ap 91725 must be taken to give a sum of 636

Answer 1

is there a comma between 91725
If your Ap is 9,17,25
Then here is your answer....

Sum of n terms of an ap is given by: S=n/2[2a +(n-1)d]
N=?(need to find out)
S=636
a=9
d=b-a=17-9=8

Substituting in the formula
636=n/2[18+(n-1)8]
1272=n[18+8n-8]
1272=n[10+8n]
1272=10n+8n²

Getting all term to one side:
8n²+10n-1272=0
Diving the whole term by 2

4n²+5n-636=0
Either using splitting the middle term or by the formula of quadratic equation.

We get n=12
Hence the sum of first 12 terms give the total of 636.

Answer 2

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