Question

13. Find the sum of the first 15 multiples of 8.
14. Find the sum of the odd numbers between 0 and 50.
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Answer 1

Answer:

The answers are:

13) 960

14) 625

Answer 2

Answer:

13) 8, 16, 24, 32, 40.....(15×8)

Starting term = 8

Common difference = 8

Last term = a+ (n-1)d = 8 + (15-1)8 = 8 + 14(8) = 120

Sum of the series = 15/2(2×8 + 14×8) = 15/2(16+112)= 15×64= 960 (ans)

14) 1, 3, 5, 7, 9.....49

Starting term = 1

Common difference = 2

Last term = 49

a+(n-1) d = 49 => 1 + ( n-1)2 = 49

=> n-1 = (49-1)/2 => n= 25

Sum of the series = 25/2(2×1 + 24×2) =25/2( 50) = 25×25 = 625(ans)

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