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# Easy arithmetic question Watch

1. The 5th term of an arithmetic series is 4 and the 15th term of the series is 39.

a) find the common difference of the series
b) find the first term of the series
c) find the sum of the first 15 terms of the series

a) Would you just use the diferrence between the 5th term and 15th term which is 10 and then the difference bettween 39 and 4 which is 35 and divide it by each other

35/10 = 3.5

b) no clue D:

c) 15/2 [2 x answer b (14) 3.5)

Anyone know formula for a) and b) part

Thanks
2. Part a looks reasonable. You don't have to use the formula if you have another valid method.

For part b, find a formula relating the nth term, n, the common difference and the first term a. You can find this formula in your formula booklet. If you don't have a copy, download one from the exam board's website. Plug in n=5, and 5th term=4 and common difference=3.5.

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Updated: December 21, 2010
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