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secondary 4 | E Maths
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Kathy
Kathy

secondary 4 chevron_right E Maths chevron_right Singapore

Thank you

Date Posted: 4 years ago
Views: 238

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Ruth Sin
Ruth Sin's answer
44 answers (A Helpful Person)
1st
Be aware of converting units to ratio! It is inverted!
E.g., if a=2b, then a:b is 2:1, NOT 1:2!
J
J
4 years ago
The other way to find the ratio without inversion :

a = 4/3 b

So a/b = 4/3

This is like saying relative to each other,
a is 4 units and b is 3 units.

So a : b = 4 : 3



Similarly,

b = 5/6 c

b/c = 5/6

And likewise, b : c = 5 : 6

Now we need to make the units the same for both ratios.

To get the simplest ratio, we find the lowest common multiple of 3 and 5, which is 15.

(3 x 5 = 15 , 5 x 3 = 15)

a : b = 4 : 3 = 20 : 15

b : c = 5 : 6 = 15 : 18

So a : b : c = 20 : 15 : 18



The technique of making the units the same is actually utilised in PSLE math.
The expression of ratio in terms of fractions is also found in the topic of similar triangle in O level E Math