Question

how many terms of the Series 15 + 11 + 7 ... has the sum 35 ?​

Answer 1

Is this ap or gp please tell it correctly

Answer 2

here,

a=15

common difference=-4

sum=35

sum=n/2[2a+(n-1) d]

35=n/2[30-4n+4]

35=n/2(34-4n)

70=34n-4n²

4n²-34n+70=0

4n²-20n-14n+70=0

4n(n-5)-14(n-5)=0

(n-5)(4n-14)=0

n=5,3.5

since the serial no of term can't come in decimal

the required answer is 5