snell's answer to dh's Primary 6 Maths Ratio Singapore question.

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snell
Snell's answer
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1st
AC : CD = 3 : 1

CD: 7u
AC: 21u


AB : BC = 5 : 2

AB: 5u
BC: 2u
AC = AB+BC = 7u

AD = AC + CD = 28u

AB/AD = 5u/28u = 5/28

AB : AD = 5 : 28


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