Question

please solve this too​

Answer 1

12)

1-2+3-4+5-6+7-8+9-10

Take all the positive terms and all the negative terms on different sides

1+3+5+7+9-2-4-6-8-10

25-(2+4+6+8+10)

25-30

=(-5)

15)(a)

30+(-25)+(-10)

30-25-10

=(-5)

(b)

(-20)+(-5)

-20-5

=(-25)