Question

Without actual addition, find the sun of the following: (i) 1+3+5+7 (ii) 1+3+5+7+9+11+13 ​

Answer 1

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We can solve it by squaring the numbers of digits.

$1. \: \: = > \: {4}^{2} \\ \: \: \: \: \: \: \: = > \: 16$

$2. \: \: = > \: {7}^{2} \\ \: \: \: \: \: \: \: = > \: 49.$

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Hope it helps.

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Answer 2

Answer:

The answers are :

i. 16

ii. 49

Step-by-step explanation:

Sum of n =n/2*2 a + (n-1) d

where n = number of terms, a = first term, d = difference between two consecutive terms.

i. sum =4/2 * 2*1 + (4-1) 2

= 4/2 * 1*2 + (3)2 = 2*(2+6) = 16

ii. sum = 7/2 * 2*1 + (7-1)2 = 7/2 * 2+12 = 49