GCSE Maths - How to Write Algebraic Expressions for Directly Proportional Relationships #90

The video tutorial explains the concept of direct proportionality using examples such as hours worked and money earned, boiling water, and wire length and diameter. It demonstrates how to write equations to express these relationships and solve problems by finding constants of proportionality. The tutorial provides step-by-step guidance on using given values to derive equations and solve for unknowns, emphasizing the importance of understanding proportional relationships in various contexts.

If the number of hours worked is directly proportional to the money earned, what would be the equation if 15 hours of work earns 180 lbs?

• E = 18H

• E = 12H

• E = 10H

• E = 15H

In the boiling water problem, if it takes 600 seconds to boil 200 grams of water, what is the constant of proportionality?

• 2

• 3

• 4

• 5

How long would it take to boil 300 grams of water if the time is directly proportional to the mass?

• 1500 seconds

• 900 seconds

• 1000 seconds

• 1200 seconds

What is the equation relating time and mass in the boiling water problem?

• T = 3M

• T = 2M

• T = 5M

• T = 4M

In the wire problem, if a wire 25 cm long has a diameter of 2 cm, what is the constant of proportionality?

• 10

• 12.5

• 15

• 20

What would be the diameter of a wire that is 50 cm long, given the length is directly proportional to the diameter?

• 5 cm

• 3.5 cm

• 4 cm

• 4.5 cm

What is the equation relating length and diameter in the wire problem?

• L = 20D

• L = 15D

• L = 12.5D

• L = 10D