3. We can see that 1+100=101 2+99=101 3+98=101 ................. and so on From 1 to 100, there are 50 pairs that has the sum is 101 Z=101×50=5050 4. We can see that 1-2=-1 3-4=-1 5-6=-1 ........... and so on There are 10 pairs that has sum is -1 Z= 10×(-1)=-10
