Question

What is the sum of a 10-term arithmetic sequence where the first term is 3 and the last term is 75?

Answer 1

390

Answer 2

y10=y1+(10-1)*d
75=3+9d
9d=72
d=8

Sn=(y1+y10)*n/2=(3+75)*10/2=78*5=390

Answer 3

formula used
n(a+l)/2
n=the number of terms
a=1st term l=last term

Answer 4

sritama was correct, thank you :):)