The coal

The coal stock would be enough to heat a larger room for 12 weeks, a smaller one for 18 weeks. It was heated for four weeks in both rooms, then only in a smaller one. How long was the coal stock enough?

Correct result:

x =  12

Solution:

$z=12a \ \\ z=18b \ \\ z - 4a -4b=b \cdot \ x \ \\ \ \\ z - 4(z/12)-4 \cdot \ (z/18)=(z/18) \cdot \ (x-4) \ \\ \ \\ \ \\ 1 - 4 \cdot \ (1/12) - 4 \cdot \ (1/18)=1/18 \cdot \ (x-4) \ \\ \ \\ 2x=24 \ \\ \ \\ x=12$

Try another example

Showing 0 comments:

Next similar math problems:

• Receiving heat
  How many degrees Celsius was an iron cylinder weighing 300 g heated in a water bath if it received heat of 7.2 kJ? (specific heat capacity of iron c = 0.46kJ/kg / ºC)
• Two rooms
  Woman cleans the room in 30 minutes a man in 90 minutes. How long will take they clean two rooms?
• Tonic
  One package tonic consume Mom 12 weeks and daughter for 14 weeks. 4 weeks they use the same cream together and then only daughter. How many weeks endured tonic to daughter then?
• Four pavers
  Four pavers would pave the square in 18 days. How many pavers do you need to add to done work in 12 days?
• Positional energy
  What velocity in km/h must a body weighing 60 kg have for its kinetic energy to be the same as its positional energy at the height 50 m?
• Pool
  If water flows into the pool by two inlets, fill the whole for 19 hours. The first inlet filled pool 5 hour longer than the second. How long pool take to fill with two inlets separately?
• Bulb
  A 60 W bulb consumes 0.12 kWh of electricity. How long did she stand light without a break?
• Pond
  A pond with two open floodgates will emptied in 20 days. A larger floodgate will emptied whole pond in 30 days. For how long would he be emptied with a smaller floodgate.
• Electric work
  Calculate the work done by the electric forces passing the current of 0.2 A through the bulb in 10 minutes if the bulb is connected to a 230 V power supply.
• Motorcycle engine
  The motorcycle engine has a constant power of 1.2 kW for 0.5 hours. How much work does the engine do? Express work in kWh and Ws units.
• Motor physics
  Car traveling at 130 km/h on the highway. Pulling power of the motor is 8 kN. Determine engine power in kW.
• Cooker
  A current of 2A passes through the immersion cooker at a voltage of 230V. What work do the electric field forces in 2 minutes?
• Construction of road
  For the construction of the road dam, it is supposed to transport six trucks a total of 18 days. After three days, two more cars were sent to the construction site. How long will it take to carry the material?
• Cows
  20 cows has food for 60 days. We reduce the dose to two-thirds for 18 cows. How many days will be fed?
• Painters 4
  One painter will do the job for 12 days. After a 4 1/3 day he comes second to help him and complete work together for 8 days. How long would work the second painter himself?
• Locomotive
  Locomotive pulled a train permanent load of 200 kN horizontally along the track of 5km. What work it done?
• Electric cooker
  During which time t does an electric cooker with power input P = 500 W and with efficiency n = 75% heat water with mass m = 2 kg and temperature t1 = 10°C to the boiling point (t2 = 100°C). The specific heat capacity of water is c = 4 180 J. Kg-1. K-1