Brainlag Plus
Brainlag PlusRatio and rates problems
Ratios that change, recipes with a limit, mixtures, average speed, density, inverse and squared proportion, and pressure.
Find one share
Most ratio problems turn on the value of one part.
- cement : sand : gravel = 1 : 2 : 4, so 7 parts in all
- 800 kg of concrete: one part is 800 ÷ 7 = 114.28... kg
- cement is 1 part: 114.3 kg, so 25 kg bags: 114.3 ÷ 25 = 4.57, round up to 5 bags
When a ratio changes (money given away, people joining), write each amount with a letter, then make an equation from the new ratio: (3x − 10) : (2x + 10) = 1 : 1 gives 3x − 10 = 2x + 10.
The rest of this lesson and its 11 practice questions are in Plus.
Screen 1 of 3, free to read.
- 11 exam-style questions, marked as you go, each with a worked solution
- Anything you get wrong is saved to your flashcards