GMATD11 wrote:

An empty pool being filled with water at a constant rate takes 8hours to fill to 3/5 of its capacity.how much more time will it take to finish filling the pool?

A. 5hr 30min

B. 5hr 20min

C. 4hr 48min

D. 3 hr 12min

E. 2hr 40 min

45-second approach: Find rate of filling. Find work remaining. Find time needed to finish: Work divided by rate equals time (to fill volume that needs filling).

What is rate of filling?

\(\frac{Work}{time} = rate\)RATE = \(\frac{(\frac{3}{5})}{8} = (\frac{3}{5}*\frac{1}{8})= \frac{3}{40}\)

How much work remaining?

\(1 - (\frac{3}{5}) = (\frac{5}{5} - \frac{3}{5})= \frac{2}{5}\)

How much time to finish remaining work?

\(\frac{Work}{rate} = time\)Work remaining = \(\frac{2}{5}\)

Rate = \(\frac{3}{40}\)

\(\frac{(\frac{2}{5})}{(\frac{3}{40})}\) =

\(\frac{2}{5} *

\frac{40}{3} = 5\frac{1}{3}hrs\)

Multiply

any fraction of an hour by 60 to get minutes.* In cases where you already have the hours, and you need hours plus minutes, use

only the fraction. (Do not include the 5 here.)

\(\frac{1}{3}hr * 60 =\) 20 minutes

\(5\frac{1}{3}hrs\) = 5 hours, 20 minutes

Answer B

*

Because:

\(\frac{1hr}{3} * \frac{60min}{1hr} =\) 20 minutes, where hours cancel
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