116
Solving word problems
Textbook: Part 4, lesson 116, pp. 19–21
GoalSolve problems step by step with the formulas for perimeter, area, volume and division with a remainder.
New words
formula · formulaexpression · ifodaconvert to one unit · bir birlikka keltirishseedling · ko‘chat
Explanation
Before solving: 1) find what is given and what is asked; 2) write the right formula; 3) write all quantities in the same unit; 4) write an expression, calculate and check the answer. One formula gives three kinds of problems: from S = a × b we also get a = S : b and b = S : a.
Worked examples
A yard is 12 m long and 80 dm wide. 80 dm = 8 m. S = 12 × 8 = 96 m².
A rectangular garden is 18 m long and 12 m wide. A seedling is planted every 2 m around it. P = (18 + 12) × 2 = 60 m, so there are 60 : 2 = 30 seedlings.
Class activity
“Pick the formula”: the teacher reads a problem. Children hold up the matching card (P, S, V, a = b × c + r) and explain why they chose it.
Practice
1
A square rug has perimeter 28 dm. What is its side in dm?
7
2
A park is 40 m long and 30 m wide. A lamp is put every 5 m around it. How many lamps are there?
28
3
A store room is 6 m long, 4 m wide and 30 dm high. What is its volume in m³? (30 dm = 3 m)
72
4
Grain was packed into 50 kg sacks: 28 sacks were filled and 35 kg were left. How many kg of grain were there?
1435