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1. How do you work out this question?
The answer is 42 apparently and it does work if you use the information given and substitute the values into the answer.
2. (Original post by Chittesh14)

How do you work out this question?
The answer is 42 apparently and it does work if you use the information given and substitute the values into the answer.
The number of yellow balls is an unknown so let's call that .

Then the number of red balls is

So the ratio of red balls to yellow balls is

Now work out how these expressions change when the balls are removed. And then write down the new ratio.

3. (Original post by Chittesh14)
...
Call the number of red balls , then:

Solve this equation/quadratic/linear equation for , take away 6 for the number of yellow, then add those two numbers to get the total.
4. (Original post by Zacken)
Call the number of red balls , then:

Solve this equation/quadratic/linear equation for , take away 6 for the number of yellow, then add those two numbers to get the total.
Thanks lol :P.
I don't know why I kept making mistakes, I obviously knew how to approach the question but for some reason I kept getting:

or even:

I kept doing this:

at the start red balls = x
yellow balls = x-6

Afterred balls = x-4
4 less red balls, so y = x - 2
then 3 yellow balls were removed so yellow balls = x - 5

Spoiler:
Show
Anyway, the way to work it out for anyone else who might want to know:

5. (Original post by notnek)
The number of yellow balls is an unknown so let's call that .

Then the number of red balls is

So the ratio of red balls to yellow balls is

Now work out how these expressions change when the balls are removed. And then write down the new ratio.

Thank you for your help. I've solved the question now.
But, I was just wondering, would this method be correct too?

Red balls = r

Where, 4 = number of red balls removed and 3 = number of yellow balls removed.

Because, if 4 red balls were removed and 3 yellow balls were removed and the ratio at the start and after the balls were removed stays the same, then that must be the ratio 4:3.

Since,

3r = 4r - 24
24 = r

number of yellow balls = number of red balls - 6 balls
y = r - 6

Then, substitute it in:

Total = t.
Total = number of red balls + number of yellow balls
Total = r + r - 6
Total = 24 + (24-6) = 24 + 18 = 42.

24 red balls
18 yellow balls
total = 42 balls

If you check it:

24:18 = ratio 4:3

After 4 red balls are removed and 3 yellow balls are removed, 20:15 = 4:3.

Ratio is same - answer is correct.

Method?
6. Oh darn, I didn't see Notnek's post! Sorry!
7. (Original post by Chittesh14)
Thank you for your help. I've solved the question now.
But, I was just wondering, would this method be correct too?

If you have a ratio and you add to and to to keep the ratio the same then = .

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