1−10+3−20+5−30+7−40+9=___
-80
-75
-88
-100
1−10+3−20+5−30+7−40+9
=(1+3+5+7+9)−(10+20+30+40)
Now, 1+3+5+7+9=52=25.
Since, the sum of first ′n′ odd natural numbers is n2.
=25−100
=−75