75
Solving word problems
Textbook: Part 2, lesson 72, pp. 66–67
GoalProblems: finding unknown parts, with units of time and length.
New words
unknown part of an operation · noma’lum komponentlight · yorug‘likplanet · sayyoraminute · daqiqa (minut)
Explanation
In a problem, words like “in how many minutes” help decide which operation is needed. Unknown parts: minuend = difference + subtrahend, subtrahend = minuend − difference, addend = sum − known addend. To compare hours and minutes, change everything into minutes: 2 h 40 min = 60 + 60 + 40 = 160 min.
Worked examples
Light takes 8 minutes from the Sun to Earth and 35 minutes more to Jupiter: 8 + 35 = 43 minutes.
If □ − 228 = 149, then □ = 149 + 228 = 377.
Class activity
“Hidden number”: a card says “934 − □ = 427”. Children find the hidden number and check on the back of the card. The one with the most correct cards wins.
Practice
1
Light takes 8 minutes from the Sun to Earth and 35 minutes more to Jupiter. How many minutes to Jupiter?
43
2
934 − □ = 427. □ = ?
507
3
The temperature on Venus is 467 degrees, which is 410 degrees more than the highest temperature ever recorded on Earth. What is that highest temperature on Earth?
57
4
How many minutes is 2 h 40 min?
160