78
Solving word problems with units
Textbook: Part 3, lesson 78, pp. 31–33
GoalSolve multi-step problems with units of length, mass and area and with equations.
New words
equation · tenglamadiagram · sxemawarehouse · omborcoal · ko‘mir
Explanation
Before solving a problem, draw the situation as a diagram and change all quantities to the same unit. Find the unknown with an equation: unknown addend = sum − known addend; unknown factor = product : known factor. Write the answer in the unit asked for and check it against the problem.
Worked examples
Three warehouses hold 750 t of grain in total. The first has 280 t, the second 245 t. The third has 750 − 280 − 245 = 225 t.
x + 14 = 3 × 9 → x + 14 = 27 → x = 27 − 14 = 13.
Class activity
“Problem workshop”: groups invent their own problem (about a warehouse, field or road), draw its diagram and pass it to another group to solve.
Practice
1
A boiler house burns 4 t 60 kg of coal a week. How many kilograms does it burn in 4 weeks?
16240
2
Find the root of the equation k − 250 = 120 : 4.
280
3
Find m in the equation (m − 6) : 8 = 7.
62
4
A plot of land is 5 ha. Onions were planted on 1 ha 40 a and carrots on 90 a. How many ares are left empty?
270
5
One sack of sugar has a mass of 50 kg. A shop received 24 sacks. How many centners of sugar is that?
12