Ricky took 30 minutes to wash the car. Derek took 50 minutes. How long would it take them to wash the car altogether?

Question

anonymous · Answer

1 hour and 20 minutes

anonymous · Answer

1/30m + 1/50m=150

australopithecus · Answer

why would it take a longer time for 2 people to wash a car? That doesn't make any sense logically.

australopithecus · Answer

Although My reasoning is probably wrong. I'm on 2 hours of sleep doing math till I pass out

anonymous · Answer

lol

anonymous · Answer

sorry thats not right, you cant just subtract their two rates to find 1 completed

anonymous · Answer

fonzy is closer, but i think you set it =1 to one, i dont remember if the fractions are setup correctly or not though

anonymous · Answer

See how problems like this one on http://www.saab.org/mathdrills/workcompletion.cgi

anonymous · Answer

Let x be the time needed for both to wash the car then
$$
\frac{1}{30}+\frac{1}{50}=\frac{1}{x}
$$
If the first can finish it in 30 minutes so in one minute he will finish 1/30 of the job.
Do the same reasoning for what follows.
Solve the above equation for x

anonymous · Answer

$$
\frac{1}{30}+\frac{1}{50}=\frac{1}{x}\
5  x + 3  x = 150\
8x = 150\
x = \frac {75}4=18.75= 18 \text { min } 45 \text { sec }
$$