Question

In an AP's if a=5 d=3,an=60 find n and sn

Answer 1

60=5+(n-1)3
60=5+3n-3
60=2+3n
60-2=3n
58=3n
n=58/3
n=19.3

sn=19.3/2(5+60)
sn=19.3/2×65
sn=19.3×32.5
sn=627.25

Answer 2

Answer:  n=16 and Sn =600

Step-by-step explanation:Given that a=15,, d=3,, and An =60

so, An=a+(n-1)d

  60= 15+(n-1)3

  60-15=3(n-1)

   45/3=n-1

   15+1=n            i.e. n=16

Now, Sn =n/2(a+An)

so, Sn= 16/2(15+60)

Sn= 8*75

Sn = 600