Question

observe the following:1+2-3+4+5-6-7+8-9=-5. change one(-) sign as(+) to get the sum 9

Answer 1

To get result 9, replace (−7) by (+7).

Thus, 1+2−3+4+5−6+7+8−9

=(1+2+4+7+8)−(3+9+6)

⇒27−18=9.