Question

Find the sum of first 10 and first 15 terms of AP:1/15,1/12,1/10....

Answer 1

Answer:

Step-by-step explanation:

a=1/15

d=1/12-1/15=5-4/60=1/60

n=10

Sn=n/2(2a+(n-1)d)

S10=10/2(2×1/15+9×1/60)

=5(2/15+3/20)

=5(8+3/60)

=5×11/60

=11/12

n=15

S15=15/2(2×1/15+14×1/60)

=15/2(2/15+7/30)

=15/2(4+7/30)

=15/2(11/30)

=11/4