Math

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3,5,-5...


The first term in the sequence of #'s shown above is 3. Each even # term is 2 more than the previous term and each odd # term, after the first, is -1 times the previous term. For example, the second term is 3+2, and the third term is (-1)x5. What is the 55th term of the sequence?

a.-5
b.-3
c.-1
d.3
e.5

The Answer is: (A)-5 H0w did they arrive at that answer???

lets look at the sequence. Check me.

3,5,-5,-3,3,5,-5, -3, 3, 5, -5, ..

Notice the terms 3, 7, 11 are all -5. So one can predict that the thirteenth term, 17, 21 term and so on will be -5.

Each fourth term after the third is -5.

the 20 +3 term is 5 spaces of 4's after 3, the 40 + 3 term is 10 spaces of 4, the 52+3 term is 13 spaces of 4, so that means the 55 term is -5

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