Question

How many rems of the ap 120,114,108... be taken so that their sum is 1260?

Answer 1

in given question
a=120,d=-6 and Sn= 1260 and we have to find n
so as Sn=n/2{2a+(n-1)d}
1260=n/2(240+(n-1)d
1260=n/2(246-6n)
1260=123n-3n^2
n^2-41n+420=0
therefore we get n=20and21
and 20 satisfied the equ there for=20 ans

thanks

Answer 2

Answer:

How many rems of the ap 120,114,108... be taken so that their sum is 1260?