Direct Proportion

Direct Proportion

Direct Proportion

If two quantities are directly proportional, then as one increases the other also increases at the same rate (proportionally), e.g. as one doubles, the other one also doubles.

Example: Jeremy uses 400 g of flour to make  8 muffins. How much flour would he need to make 30 muffins?

Multiple Choice

A packet of 500 sheets of paper has mass 2.5 kg.

Find the mass of one sheet of paper ?

• 200 kg

• 200 g

• 5 kg

• 5 g

Proportionality Constant

If two quantities, y and x are directly proportional, we can write

y ∝ x

y = kx

k - proportionality constant

Multiple Choice

Y is directly proportional to X, when Y=8, X=4. Find the equation relating Y and X.

• Y=X

• Y=kX

• Y=2X

• Y=0.5X

Multiple Choice

If c varies directly as the square root of d, and c = 4 when d = 256, find c when d = 400.

• 10

• 5

• 20

• 80

Graph of direct proportion

Multiple Choice

Which of the following graph shows a direct proportion relationship?

Multiple Choice

Which graph shows a direct proportion ?

• Graph of taxi A

• Graph of taxi B

Tables

Multiple Choice

The distance a body falls from rest varies directly as the square of the time it falls (ignoring air resistance). If a ball falls 144 feet in three seconds, how far will the ball fall in seven seconds?

• 112

• 16 feet

• 628

• 784 feet