Question

The Value of the expression 2-11+4-12+6-13+......... till 100 terms is .

Answer 1

Considering the pattern in the given information, the left side is an Arithmetic Progression with common difference 1, and the right side is a progression with increasing common difference of 2 (6+6, 12+8, 20+10 etc). So the answers can be:
7=42+14=56
8=56+16=72
9=72+18=90 and so on.
So 56 should be equal to 7, 72 should be equal to 8 and 90 should be equal to 9 and vice - versa.
Coming to the value of 81, it doesnt set into the pattern, but may be we can choose the mid value of 72 and 90 which gives the answer as 8.5

So final answers,
9=90
56=7
81=8.5
72=8
90=9