Question

1-2+3-4+5 ........ -100 =??
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Answer 1

1-2+3-4+5 ........ -100 =  -50

Step-by-step explanation:

1-2+3-4+5 ........ -100 =

Simple method

out fo 100 numebrs lets makes 50 pairs

(1 - 2) + (3 - 4) + (5 - 6) +........................+(99 - 100)

= (-1) + (-1) + (-1)  +...............................(-1)

= -50

1-2+3-4+5 ........ -100 = -50

Long way

1-2+3-4+5 ........ -100

= (1 + 3 + 5 +......................+99)  - (2  + 4 + 6 +...................+ 100)

using Sum of an ap = (n/2)(a + L)

n = number of terms

a = first term

L = Last term

= (50/2)(1 + 99) - (50/2)(2 + 100)

= 25 ( 100 - 102)

= 25(-2)

= -50

Learn More:

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Answer 2

$\star$ Answer :

$\star$ 1 - 2 + 3 - 4 + 5 - ........ + 99 -100 = - 50

$\star$ Step-by-step explanation :

$\star$ 1 - 2 + 3 - 4 + 5 - ........ + 99 - 100

$\star$ => (1-2)+(3-4)+(5-6)+........(99-100)------> 50 terms

$\star$ =>(-1)+(-1)+(-1)+(-1)+(-1)+(-1)+.......--------> 50---> (-1)'s

$\star$ => - 50

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