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A light bulb consumers 4560 watt-hours in 4 days and 18 hours. How many watt-hours does it consumer per day?

User BoooYaKa
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1 Answer

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Realize that 4 days and 18 hours need to be converted into hours to give the answer.

So we reduce 4 days to hours: 4 * 24 = 96 hours and add to this the other 18 hours to obtain a total of: 96 + 18 = 114 hours.

So now we can divide the watage consumed per hour is: 40, and then the watage consumed per day will be this number times 24 (since there are 24 hours in one day):

40 * 24 = 960 watt-hours per day.

You could have answered it also reducing the consumption time to days, but it gives a decimal which is more complex to handle in the first step

The next problem involves a copy machine that makes 36 copies per minute and we are asked how many copies it will make in 5 minutes and 30 seconds.

So again we need to convert the quantity wich is given in two different units (minutes and seconds) into a single unit (preferably minutes since the other info is in minutes)

Then recall that 30 seconds is HALF a minute (0.5 minutes) then 5 minutes and 30 seconds is the same as 5.5 minutes.

Now we do the following proportion :

If 36 copies are done in one minute, then X copies will be done in 5.5 minutes

In math terms, it is the same as:

36 is to one, the same as x is to 5.5

and is written as:

36 / 1 = X / 5.5

to solve for X in this equation, we multiply both sides by 5.5 that way we isolate X on the right:

36 * 5.5 = X

Then X = 198 copies.

I think your teacher wants you to start using this type of proportions to solve problems involving rates.

User Anton Khirnov
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