Question

12. Find the value of: 1- 2 + 3 - 4 + 5 - 6 + 7 - 8+
-20.
[Hint. Pairing the numbers, we have required sum =
(1 -- 2) + (3 - 4) + (5 - 6) ... (19 - 20) = (-1) + (-1) + (-1 +
+ (-1). There being 10 terms in all = -10.)
3. Calculate the sum: 3 + (-3) + 3 + (-3) + 3+ (-3) + ...
terms is 15.​

Answer 1

Answer:

Step-by-step explanation:

First Paire the numbers

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

(-1)+(-1)+(-1)+(-1)+(-1)+(-1)+(-1)+(-1)+(-1)+(-1)+(-1)+(-1)+(-1)+(-1)(-1)+(-1)+(-1)+(-1)+(-1)+(-1)

= -20

3 . 3-3-3-3-3-3-3-3-3-3-3-3-3-3-3

   = -45

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