A fast way to sum a series of numbers
@(biswajit16.blogspot.com)
Here's a quick way to sum a sequential series of numbers.
If you want to add a sequential series of numbers you may do so by multiplying the exact middle number by the number of them to be added, such as:
10+11+12+13+14+15+16+17+18+19+20 = 15 x11 = 165
15 = the middle number in the series
11 = the number of numbers in the series
Notice the above sequence had an odd number of items, so it had an exact middle number. What about a sequential series with an even number of items? Simply take the average of the middle TWO numbers, like so:
26+27+28+29+30+31+32+33+34+35 = ((30 + 31)/2) x 10 = 30.5 x 10 = 305
30.5 = (30 + 31)/2 = the average of the middle two numbers in the series
10 = the number of numbers in the series
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