The idea
A multi-step problem must be broken into connected calculations in a sensible order.
Follow these steps
- Identify the final quantity required.
- Write the intermediate quantities needed to reach it.
- Calculate one stage at a time, keeping units and checking the final result.
See the method in action
Example 1
Of 28 pupils, 12 play chess, 14 play tennis and 3 do both. How many do neither activity?
- Adding the activity totals counts the 3 pupils in both groups twice.
- The number doing at least one is 12+14−3=23.
- Subtract this from 28 to obtain 5.
Example 2
A tank with vertical sides and a constant horizontal cross-section holds 720 litres at a depth of 80 cm. Water is removed and the depth falls by 20 cm. How much water remains?
- The new depth is 60 cm.
- Each centimetre of depth represents 720 ÷ 80 = 9 litres, so 60 × 9 = 540 litres remain.
A useful shortcut
Calculate one stage at a time, keeping units and checking the final result.
Watch out for these
Three fresh questions
Ready to check the method? You will get three fresh, validated questions.