(6) Find the sum of all two digit odd multiples of 3.
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Answered by
1
Answer:
ap=12, 15,18,..........99
an=12+{n-1) 3
99 = 12+3n-3
99=9+3n
99-9= 3n
90=3n
n=30
S30 = 30/2(2×12+(30-1) 3)
= 15(24+87)
= 15×111
S30 = 1665
Answered by
0
15,21,...,99
=a +(n - 1) d
99 = 15 + 6n - 6
n = 15
sum of ap = n÷2 (2a +(n - 1) d)
= 15/2 ( 6 +14×6)
= 855
sum is 855
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