wordmath problem
posted by Michael .
Assume that the amounts of oil produced by the first, second, third, ..., wells in a new oil field form a decreasing geometric sequence. If the first well produces 80,000 barrels and the second produces only 70,000 barrels, predict the total amount of oil that could be produced from the field if many wells are drilled.

a = 80,000
r = 7/8
infinite sum is a/(1r) = 80,000/(1/8) = 640,000