SOLUTION: Heater A warms a room from 40 degrees to 70 degrees in 5 hours. Heater B can do this job in 7 hours. Heater A alone is started but breaks down in 2.5 hours. How long will it take h

Algebra ->  Rate-of-work-word-problems -> SOLUTION: Heater A warms a room from 40 degrees to 70 degrees in 5 hours. Heater B can do this job in 7 hours. Heater A alone is started but breaks down in 2.5 hours. How long will it take h      Log On


   

Question 1032872: Heater A warms a room from 40 degrees to 70 degrees in 5 hours. Heater B can do this job in 7 hours. Heater A alone is started but breaks down in 2.5 hours. How long will it take heater B to finish the job.
* a chart would be especially helpful*
Answer by josgarithmetic(39625) About Me  (Show Source):
You can put this solution on YOUR website!
The exercise is intended as a uniform rates problem, each "worker" being a heater, working at its own rate. You can make a chart or table of rates.

One job is "warm the room air from 40 to 70 degree". 

HEATER          RATE

A               1/5

B               1/7


Another chart may be what you want, but the rest of the solution will be through equations only. The rule to use will be RT=J relating rate, time, job.

highlight_green%28%281%2F5%29%282.5%29%2B%281%2F7%29x=1%29 for the heaters working separately, to do ONE JOB. The unknown time for heater B to work to finish the job is x.

Once that is understood, solving for unknown time x is uncomplicated arithmetic.