Direct Proportion
Direct and Inverse Proportion · Class VIII
When y = k x, slide the constant k and see how y grows with x.
- y at sample6
- Ratio y/x2
- y = k x
Formulas in this lab
- y at sample
- Ratio y/x
Frequently asked questions
▶What is direct proportion?
Two quantities are in direct proportion if y = k*x, meaning when x doubles, y also doubles. The constant k is the ratio y/x. For y = 50 when x = 5, k = 10, so y at x = 8 is 80.
▶How do I use the direct proportion lab?
Slide the constant k (0.1 to 10) and sample x. The lab shows y = k * x and confirms the ratio y/x is always k. Try k = 4 and x = 7 to see y = 28 and ratio 4.
▶Where do I see direct proportion in Indian shops?
Buying oranges: if 1 kg costs Rs 80, 3 kg costs 80 * 3 = Rs 240, and 5 kg costs Rs 400. Here k = 80 (rupees per kg). The lab lets you set k to any per-unit rate and compute totals quickly.
▶Direct vs inverse proportion: how to spot which?
Direct: as one goes up, the other goes up at the same rate (more time means more pay). Inverse: as one goes up, the other goes down (more workers means less time per task). The lab handles the direct case; for inverse, use the inverse proportion lab and watch y fall as x grows.