89
Solving word problems
Textbook: Part 3, lesson 84, pp. 26–27
GoalSolve problems about perimeter and area; bring units to the same size.
New words
wall · devorarea · yuzperimeter · perimetrunit of measure · o‘lchov birligi
Explanation
First decide whether the problem asks for the perimeter or the area. Perimeter is measured in cm, dm, m and area in cm², dm², m². Before adding different units, change them to the same unit: 2 dm² + 45 cm² = 200 cm² + 45 cm² = 245 cm². A wall 5 m wide and 3 m high has perimeter 5 + 3 + 5 + 3 = 16 m and area 5 + 5 + 5 = 15 m².
Worked examples
5 m² − 120 dm² = 500 dm² − 120 dm² = 380 dm².
A craftsman worked 3 h 40 min: 60 + 60 + 60 + 40 = 220 minutes.
Class activity
“Perimeter or area?”: the teacher reads a problem. Children hold up a “P” (perimeter) or “S” (area) card and say the unit.
Practice
1
A wall is 5 m wide and 3 m high. What is its perimeter in metres?
16
2
What is the area of this wall in m²? (3 rows of 5 m²)
15
3
145 cm² + 2 dm² = ? cm²
345
4
5 m² − 120 dm² = ? dm²
380
5
A craftsman worked 3 h 40 min on day one and 2 h 35 min on day two. How many minutes in total?
375