Question 50375
28+35+42+49+......728.


The sum is the average of the 1st and last terms times the number of terms.

S=(1/2)n(1st + last)
Need to find number of terms, as follows:
728-28=700
700/7 = 100
So, 728 is the 100th term.

S=1/2(100)(28+728)
S=50(756)
S=37,800

Cheers,
Stan H.