PROPORTION

Given that y is proportional to x, find the missing values of y

x 2 5 10 20 50

y 18

PROPORTION

The current, I, in a particular wire is proportional to the voltage, V. If I = 8 amps when V = 5 volts then find

(a)The current when the voltage is 8 volts

(b) The voltage if the current is 10 amps.

PROPORTION

There can be other ways in which two variables are directly proportional to each other.

Consider the formula for the area of a circle……

2rA A is directly proportional to the SQUARE of the radius. The constant k = 3.14….

PROPORTION

Other relationships to consider….

2xy

xy

y varies directly with the square of x

y varies directly with the square root of x

EXAMPLE

It is known that a is proportional to the square of n. Complete the table…

n 2 5 8 20

a 8 200

EXAMPLE 2

If a stone is dropped from the top of a building, the time t, to reach the ground is proportional to the square root of the height h of the building. Given that a stone takes 4.5 secs to fall 100 feet, how long will it take to fall 50 feet?

COMMON MISTAKE ! Do not halve the time!!!!!

FIND THE CONSTANT OF PROPORTIONALITY FIRST