Question

Which term of the sequence 3, 8, 13, ........ is 78 ?

Answer 1

Let a=3
d=5, (8-3)=5
an=78
78 = a+(n-1)d
78=3+ (n-1)5
78=3+5n-5
78=-2 +5n
78+2=5n
80=5n
n=80/5
n=16


Answer is 16.....