math question

[USAFfiredog]

How do u solve this math question.
Mike can wash a fire truck in 30 mins. Mike and tom can wash a truck in 20 minutes. How long does it take tom to wash.the.truck alone?

[fire49]

20 minutes

[KB1OEV]

How do u solve this math question.
Mike can wash a fire truck in 30 mins. Mike and tom can wash a truck in 20 minutes. How long does it take tom to wash.the.truck alone?

The answer is that Tom takes 60 minutes to wash the truck alone.

Method:

Mike can wash 1 truck in 30 minutes. From this we can determine that in the 20 minutes he is washing the truck with Tom, Mike will have washed 2/3 of the truck himself (1 truck in 30 minutes = 1/3 of the truck every 10 minutes).

If Mike washes 2/3 of the truck in 20 minutes, and he and Tom finish at the same time, then Tom will have had to wash the remaining 1/3 in the same 20 minutes.

If Tom can wash 1/3 of the truck in 20 minutes then he will need 60 minutes to wash the whole thing.

[technotech]

yea nice question btw.. i also calculated it 60 minutes as i am good in maths

[jgraham]

I struggled with math (and a bunch of other topics for the written test). The best book I found was Lepore's book Smoke Your Firefighter Written Exam. He teaches how to work out every type of math scenario you could ever see. I no longer worrk about written tests....