Skip to 0 minutes and 4 secondsThe problem here is to distinguish which cake weighs heaviest. Cake one, which is 3/17 of a 2.7 kilogramme cake, or cake two, 2/13 of a 3.1 kilogramme cake. The difficulty here arises from the fact they you have different proportions of different cakes with different masses. So in fact, if you multiply 3/17 by 2.7 kilogrammes, you will get the mass of cake one that you have. So 3/17 multiplied by 2.7 kilogrammes equals 0.4764 kilogrammes. Similarly for cake two, if you multiply 2/13 by 3.1 kilogrammes, you will get the mass of cake two that you have. So 2/13 multiplied by 3.1 kilogrammes equals 0.4769 kilogrammes.
Skip to 1 minute and 9 secondsAs you can see these two masses are very similar, and it would have been extremely difficult to determine this without this piece of mathematics. But by comparing the two numbers, you can see that cake two is the heaviest.
Solution to the cake question
The video here gives the solution to the questions in the previous step comparing the weights of two cakes.
Have a go at another problem. For this question you need to know that 1lb = 454g and 14lbs = 1 stone.
There are three people from different countries which use different measurements to determine their weight. Work out which of the three is the heaviest: An English man weighing 13st 5lbs, an American man weighing 191 lbs or a French man weighing 88.3kg.
The answer is in the video in the next step.