Sum of all natural numbers from 100 to 1000 which are multiples of 5
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=105+110+115+120+..............+995.
=a=105
=d=5
=tn=a+(n-1)d
=995=105+(n-1)×5
=995=105+5n-5
=995=100+5n
=995-100=5n
=885=5n
=n=177
=S177=n/2[a+l]
=S177=177/2[105+995]
=S177=177/2×1100
=S177=177×550 ans
=a=105
=d=5
=tn=a+(n-1)d
=995=105+(n-1)×5
=995=105+5n-5
=995=100+5n
=995-100=5n
=885=5n
=n=177
=S177=n/2[a+l]
=S177=177/2[105+995]
=S177=177/2×1100
=S177=177×550 ans
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