Video Transcript
Write the answer to the calculation
in grams. Three and three-quarter kilograms
subtract 640 grams.
When we look at this question, we
notice that our masses are given in different units. We have a value in kilograms and a
value in grams. We therefore need to convert
between the two units. We’re asked to give the answer to
our calculation in grams, so it will be sensible to change this unit in kilograms
also into grams. We can recall that in one kilogram,
there are 1000 grams. When we have a value like three and
three-quarters with a fraction, there are several different ways in which we can
think of converting this into grams. One way might be by splitting our
three kilograms and our three-quarter kilograms. If one kilogram is equal to 1000
grams, then we would take our unit in kilograms and multiply it by 1000 to get the
equivalent in grams. So therefore, three kilograms would
be three times 1000 grams. And that’s of course 3000
grams.
To work out three-quarters of a
kilogram into grams, that would be working out three-quarters of 1000 or
three-quarters times 1000. We might recall that a half of 1000
is 500. So a quarter of 1000 would be the
same as half of 500. And that’s 250. So in order to work out
three-quarters of 1000, we could think of it as multiplying a quarter by three or,
indeed, by adding a half and quarter. Either of those would give us 750
grams. So if three kilograms is 3000 grams
and three-quarters of a kilogram is 750 grams, adding those together would give us
that three and three-quarter kilograms is 3750 grams.
The other approach to this question
is to work out what three-quarters is as a decimal first. As three-quarters is equal to 0.75,
then three and three-quarters is 3.75 kilograms. In order to change this value into
grams, we’re still going to need to do the same multiplication by 1000. When we multiply by 1000, we move
our digits three places to the left, which will give us 3750 grams, the same as we
calculated in the first method. We can then go ahead and work out
the answer to this subtraction. 3750 subtract 640 gives us the
answer in grams of 3110 grams.
