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## Answers

You can use manual addition or the formula for the summation of arithmetic series; which is:

Sn = n [2a + (n-1)d] all over 2

where n = 10 since there are 10 odd numbers from 1 to 20

a = 1 which is the first term in the arithmetic series

d = 2 which is the distance between the terms *3-1=2

Sn = 10 [2(1) + (10-1)2] all over 2

Sn = 10(2+18) all over 2

Sn = 10(20) all over 2

Sn = 200/2 = 100

100 is the sum of all the numerators

Now we divide it by the denominator 2; 100/2 = 50

The answer is 50