yellowho wrote:9+19+29+39+49+ . . . +979+989+999=
Is there a way to do this with combination?
To determine the sum of evenly spaced integers, I find it easiest to use the following formula:
Sum = (number of integers) * (average of biggest and smallest)
To count the number of evenly spaced integers in a set:
Number of integers = (Biggest - Smallest)/(distance between each successive pair) + 1
Thus, given the integers from 9 to 999, inclusive, with a distance of 10 between each successive pair:
Number of integers = (999-9)/10 + 1 = 100.
Average of biggest and smallest = (999+9)/2 = 504.
Sum = 100*504 = 50,400.
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