See Matthew Soon's answer to Blursotong's Primary 6 Maths Data Analysis Singapore question

Matthew Soon's answer to Blursotong's Primary 6 Maths Data Analysis Singapore question.

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Trial and Error method:

At the start,

$2:$10
5 : 2

We try building a table of guesses to trial and error:

$2 | $10 | After exchange
5 , 2 》 15 , 0 (not possible to have ratio)
10 , 4 》 20 , 2 (the ratio is now 10:1)
15 , 6 》 25 , 4 (the ratio is now 25:4)
20 , 8 》 30 , 6 (the ratio is now 5:1) 《 correct

Tim had 8 $10 notes at first.

Algebra method:

Initial $2:$10 is 5x to 2x.

The exchange of notes and new ratio may be expressed as:

(5x+10)/(2x-2) = 5/1
10x-10 = 5x+10
5x = 20
x = 4

So Tim had 2(4) = 8 $10 notes at first.

Date Posted: 4 years ago

Comments 2 add a comment

Blursotong

4 years ago

Appreciate your help. I roughly understand the trial and error method but I am totally lost with the algebra one, haha. But thank you again!

Matthew Soon

4 years ago

It's okay, at this stage you're more or less expected to be familiar with the trial and error method instead.

I can explain the algebra one a little bit more if you are interested to understand (posting a separate answer).