If the tolerance of arithmetic sequence {an} d = 1 / 2, a1 + A2 + a3... + A99 = 60, calculate S100

If the tolerance of arithmetic sequence {an} d = 1 / 2, a1 + A2 + a3... + A99 = 60, calculate S100

S99=(a1+a99)*99/2=60
a1+a99=60*2/99
S100=(a1+a100)*100/2=[a1+(a99+d)]*50=(a1+a99)*50+50d
=50*60*2/99+25
=2825/33