Answer:
= 12.5
Step-by-step explanation:
This is equivalent to
20*(1 - 1/2 + 1/4 - 1/8 + ...)
= 20*[(1 + 1/4 + 1/16 + ...) - (1/2)(1 + 1/4 + 1/18 + ...)]
= 10*(1 + 1/4 + 1/16 + ...)
= 10 * (4/3) = 40/3 or 13.333...
To check for a gross error, notice that 20 - 10 + 5 - 5/2 = 12.5, so we are certainly in the correct general range (suggesting that my answer is in fact correct).
