find the sum of multiples of 7 between 100 300
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Answer:
7805588588558558886
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In this interval
1st no.=105
Last no.=294
difference (d)=7
an=a1+(n-1)d
where
a1=105
an=294
d=7
294=105+(n-1)7
=105+7n-7
=105-7+7n
=98+7n
294-98=7n
196=7n
n=196/7
=28
Sn is the sum of n terms in arithmetic progression.
Sn=(n/2)(a1+an)
n=28
Sn=(28/2)(105+294)
Sn=14×399
Sn=5586
The sum is5586.
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