Video: GCSE Mathematics Foundation Tier Pack 3 • Paper 1 • Question 24

GCSE Mathematics Foundation Tier Pack 3 • Paper 1 • Question 24

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Video Transcript

Five bars of soap have a total weight of 750 grams. Four bottles of soap have a total weight of 600 grams. Calculate the total weight of four bars of soap and six bottles of soap. Give your answer in kilograms.

In order to be able to answer this question, we first need to work out the weight of a single bar of soap and a single bottle of soap. We’ll start with the bars. We’re told in the question remember that five bars of soap have a total weight of 750 grams.

To find the weight of one bar, we need to divide 750 by five, which we can do using a short division or bus stop method. There is one five in seven with a remainder of two, there are five fives in 25 with no remainder, and there are no fives in zero. So 750 divided by five is 150.

We’ve worked out then that one bar of soap has a weight of 150 grams. But we need to find the weight of four bars of soap. To find this then, we need to multiply 150 by four, which is the same as doubling it and then doubling it again. Doubling 150 gives 300 and that’s because doubling 15 gives 30 and then doubling 300 gives 600. So we found that the weight of four bars of soap is 600 grams.

Next, let’s consider the bottles. We’re told in the question that four bottles of soap have a total weight of 600 grams. To find the weight of one bottle then, we need to divide 600 by four. We could do this by halving and then halving again, but there’s actually an easier way.

Earlier in the question, we saw that 150 multiplied by four was 600. So the reverse of this means that 600 divided by four is 150. And this gives us the answer to the calculation that we’re looking for. So the weight of one bottle of soap is 150 grams. But we need to work out the weight of six bottles of soap.

To find this, we need to multiply 150 by six. We could do this using a column multiplication method or we can be a little bit smart about this. We already know that four multiplied by 150 is 600. And we can work out that two multiplied by 150 is 300. So to find six multiplied by 150, we just need to add these two values together. And it gives 900. This tells us then that the weight of six bottles of soap is 900 grams.

We then just need to add the total weight of the four bars and the six bottles together, which we can do using a column addition method. 600 plus 900 is 1500. Remember though that this is 1500 grams. And the question asks to give our answer in kilograms.

There are 1000 grams in a kilogram. So to convert this answer in grams into a value in kilograms, we need to divide by 1000. To do so, we can keep the decimal point, which in this case would be at the end of the number, fixed and move all of the digits three places to the right. So 1500 divided by 1000 is equal to 1.5.

The total weight of four bars and six bottles of soap is 1.5 kilograms.