Simon is mixing concrete as part of a DIY project at home. Concrete is made by mixing aggregate (a premixed gravel/sand mix) with powered cement. The ratio of aggregate to cement is 3:1
Simon has 15kg of aggregate in the wheelbarrow, and another 15kg in a bag.
How many kg of cement powder should he add to all of his aggregate in order to get the right ratio to make concrete?
Students find this problem quite straight forward, although they must realise the total of aggregate that is available, and not just what is in the wheelbarrow. By emphasising ‘how much is one portion’ in the ratio, the numbers are easy to work out. This is often solved in only 2-3 mins.
Teachers could extend the learning by considering:
- Clarice needs to make 100 kg of concrete for her project. How many kg of aggregate and cement should she buy?
- Without using aggregate, the full ratio of sand to gravel to cement is 2:4:1. George has some sand (25kg) and cement (15kg) left over from a previous job. How much gravel would George need to buy? What would be the most amount (kg) of concrete he could make by only buying sand and using the other amounts his has already?