A bag contains red and blue counters in the ratio 1:3.
When four red counters are added to the bag, the ratio changes to 1:2.
Work out the number of blue counters in the bag.
Total counters = x + 3x = 4x
Blue counters = 3x
New total of red = x+4
So Red counters (x+4) : Blue counters (3x) [Ratio is x+4 is to 3x]
This ratio is the same as the ratio 1:2 [given in the question]
If two things (such as a,b) are in the ratio 1:2, 2a is always equal to b. If you don't believe it, think about:
4:8 OR 3:6 This is a very useful standard rule for any a,b.
So 2(x+4) = 3x
2x + 8 = 3x
x = 8
At the start we said that x is the number of red counters and the questions says that R:B is ratio 1:3.
So B is three times R, which is 3x8 which is 24 -- your answer.
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