Question

calculate 1-2+3-4+5-6+7-8.........19-20​

Answer 1

Step-by-step explanation:

take two terms one by one and bracket it.like

(1-2)+(3-4)+(5-6)+(7-8)+..........+(19-20)

= -1-1-1-1-...-1

now think you made 10 brackets because here is 1-20 and you paired up with each two.that means you have 10 no of -1.so your answer is 10*(-1)=-10

Answer 2

Answer:

1-2+3-4+5-6+7-8+9-10+11-12+13-14+15-16+17-18+19-20

= - 110 + 100

= - 10

hope it will help u... ☺️