If the first term in an arithmetic series is 3, the last term is 136, and the sum is 1390, what are the first 3 terms?

Question

anonymous · Answer

first 3 terms are 3,10,17
you add 7 
to find this take 136-3 which is 133 and then find what divides 133 so there are no decimals.

anonymous · Answer

but 19 also divides 133, so cant it be add 19? and then it would be 3, 24, 43?

anonymous · Answer

it does, but if you do the math, using 19 as the additive does not sum up the terms to 1390.

anonymous · Answer

to find the sum of an arithmetic series, use the formula $$s_n=(n(a_1+a_n))/2$$

anonymous · Answer

$$s_n$$ is your sum, n is the number of terms, $$a_1$$ is your first term, and $$a_n$$ is your last term

anonymous · Answer

after finding n, then you can use the equation $$a_n=a_1+(n-1)d$$ 
and solving for d gives you the difference between terms

anonymous · Answer

got it thanks!