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Delete - Last Modified By: dna at 29/04/2014 1:01:18 PM
The following link takes you to an exercise from a textbook, Maths Zone 8. There are worked examples as well as a series of practice problems to try.
Edit Delete - Last Modified By: dna at 29/04/2014 1:07:17 PM
Edit Delete - Last Modified By: dna at 29/04/2014 1:16:38 PM
Khan Academy link....
Edit Delete - Last Modified By: dna at 4/05/2014 10:00:50 AM
Some notes and worked examples.....
Edit Delete - Last Modified By: dna at 4/05/2014 10:01:13 AM
Ratios or scales are written to the same units, for example, 1:10 000 can be read as:
1 cm to 10 000 cm' or even 1 m to 10 000 m
That's because the ratio is just telling us that one is 10 000 times bigger than the other. The units must however be the same in order for this to work. You can change the units to make life a little easier if you like. The examples above would then become:
1 : 10 000
1 cm Û 10 000 cm
which simplifies to 1 cm Û 100 m notice the change in symbol
Example.....
If a scale of 1 : 100 is used to draw a plan of a room, what does a wall of 5 cm on the plan represent in real life?
1 : 100 the plan is in cm, so lets use cm in our ratio, then
1 cm Û 100 cm but we have 5 cm on the plan, so
5 cm Û 500 cm now convert to more appropriate units
5 cm on the plan represents 5 m in real life.
Example......
A photo measures 6 cm by 4 cm and is enlarged by a factor of 3 : 1. What is its new size?
Scale factor is 3/1 = 3, so each side is 3 times larger
6 ´ 3 = 18 and 4 ´ 3 = 12.
the new size is 18 cm by 12 cm.
Edit Delete - Last Modified By: dna at 4/05/2014 10:10:34 AM