Find the sum of each the following. ( ANSWER ALL PLEASE )

1. multiples of 3 from 15 to 45


2. numbers between 1 ang 81 which are divisible by 4


3. first 20 terms of the arithmetic sequence -16, -20, -24,...


4. first 10 terms of the arithmetic sequence 10.2, 12.7, 15.2, 17.7,...

5. 1 + 5 + 9 ... + 49 + 53

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Answers

2016-07-10T15:19:53+08:00
1.)
a1=15,an=45,d=3,
n=an-a1/d +1
n=45-15/3+1
n=30/3+1
n=11
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