Lesson 9 of 15
When two amounts grow together
Show on a big screenRice costs ₹40 a kilogram. A taxi charges ₹50 to start and then ₹12 a kilometre.
Loading lab…
Step 1 of 3
- Rice, row by row: the bar climbs.
- Bill ÷ kg = 40, every row — direct proportion.
- Taxi: 62, 37, 28.7, 24.5 — the line bends.
The rule
Put each pair of amounts in a row. Divide one amount by the other, row by row. If the answer never changes, the amounts are in direct proportion.
- Rice costs ₹40, ₹80 and ₹120 for 1, 2 and 3 kg. Dividing by the kg gives 40, 40 and 40.
- Taxi: 50 + 12 = ₹62 for 1 km. And 50 + 24 = ₹74 for 2 km. Then 62 ÷ 1 is 62 and 74 ÷ 2 is 37. Not the same.
Watch out!
Both amounts rising is not enough. The taxi bill and the distance both rise, but bill ÷ km changes.
Try the lab to finish this lesson.