The Student Room Group
Reply 1
tot=0

for i=101:400;
tot=i+tot;
end

tot = 75150

the mark books right.
just put the numbers into the arithmetic equation whcih ive forgotten and you should get the same answer.
Reply 2
Sn= 0.5n(2a+(n-1)d)

S(400)= 0.5*400(2+(399)1) = 200*401=80200
S(100)=0.5*100(2+99(1))=50*101=5050
Sum between 101 and 400 = S(400)-S(100)=80200-5050=75150

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