Answer:
20
Step-by-step explanation:
The ratio of red : yellow is 3 : 4 = 3x : 4x ( x is a multiplier )
If 3 red counters are removed then
red : yellow = 3x - 3 : 4x = 3 : 5
Expressing in fractional form
[tex]\frac{3x-3}{4x}[/tex] = [tex]\frac{3}{5}[/tex] ( cross- multiply )
5(3x - 3) = 12x
15x - 15 = 12x ( subtract 12x from both sides )
3x - 15 = 0 ( add 15 to both sides )
3x = 15 ( divide both sides by 3 )
x = 5
Then
number of yellow counters = 4x = 4 × 5 = 20