A factory makes rods by cutting platic pipes that are 5 feet long into 8 rods. How long is each rod

If you divide 8 by 5 you should get 1.6

The first and third selections are infinite sums. The given sum is finite, so those choices are incorrect.

The second choice fails to give the correct value for n=0. (It gives 0, not -3.)

Thus, all choices are eliminated except the last one. It gives the summation of the correct terms for the correct number of terms.

The 4th selection is correct: