Lesson 8 of 14
Workers and days, speed and time
Show on a big screen6 people paint a hall in 12 days. How long do 9 people take?
Step 1 of 3
- 6 × 12 = 72.
- 72 ÷ 9 = 8 days.
- Check: 9 × 8 = 72.
If everyone works at the same speed, 9 people take 8 days.
Rule: Multiply the pair you were given. Divide by the new amount. Multiply back — it must give the same number.
The given pair is 6 people and 12 days. Their product is 72. The new amount is 9 people. The product stays 72. So 9 people take 72 ÷ 9 = 8 days.
A road is 180 km long. A speed of 60 km/h means 60 km in each hour. At 60 km/h the trip takes 3 hours, because 60 × 3 = 180. The road stays 180 km. So at 40 km/h it takes 180 ÷ 40 = 4.5 hours. Check: 40 × 4.5 = 180.
Drag the new crew. Read the three steps.
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Try the lab to finish this lesson.