The presentation includes all the necessary material for review of Chapter 21 Proportions for IGCSE Mathematics Cambridge International Examinations. It will be useful for students as the review materials and also for teachers as the teaching tips and presentations in the class.
The presentation was made by Oleksii Khlobystin (Alex) - Mathematics Teacher at Depu Foreign Language School, Chongqing City, China.
Personal website: www.visualcv.com/o-khlobystin
Personal email: o-khlobystin@yandex.comPresentation POWER POINT Chapter 21 Proportions, IGCSE Mathematics CIE 0580
Made by Oleksii Khlobystin
Personal website: www.visualcv.com/o-khlobystin
Personal email: o-khlobystin@yandex.com
Made by Alex
“Proportions”
express direct and inverse variation in algebraic
terms
use algebra to find unknown quantities in
direct/inverse variation problems
increase and decrease a quantity by a given
ratio
Direct Proportion
x
y
0
0
1
2
2
4
3
6
5
10
12
24
Y is directly proportional to X:
y ??? x
That is, y = x multiplied by a constant:
y = kx
Take an example: 4 = 2x k = 2, so y = 2x
Direct Proportion
e.g. y is directly proportional to x.
When x = 2, y = 8. Find x when y = 10.
Direct Proportion
e.g. y is directly proportional to x2.
When x = 2, y = 16. Find x when y = 5.
???
???
???
???
Inverse Proportion
e.g. y is inversely proportional to x.
When x goes up, y goes down.
Inverse Proportion
e.g. y is inversely proportional to x2.
When x = 2, y = 1. Find y when x = 1.
???
y =
y = ???
Using direct/inverse proportion
to solve problems
Mr. Jones wants to build a patio. It will take 3 men 72
hours to do it. How long will 5 men take?
Is this direct or inverse proportion?
h ???
???
Using direct/inverse proportion
to solve problems
The power (P) generated in an electrical circuit is
proportional to the square of the current (I) amps.
When P = 108, I = 6. Find I when P = 75.
???
???
???
???
???
Increase and decrease by a
given ratio
e.g. increase 200 by a ratio of 3:2
“allow three parts for every two”
Increase and decrease by a
given ratio
e.g. decrease 210 by a ratio of 3:7
=
Increase and decrease by a
given ratio
5:3
3:5
2:3
2:1
decrease
decrease
increase
increase
2:2
3:5
6:1
6:2
identity
decrease
increase
increase
Increase and decrease by a
given ratio
This postcard is enlarged by 5:2. What are
the new dimensions?
1
6
c
m
10 cm
??? cm
??? cm
IGCSE Ch21 Proportions ALEX.ppt
