High School

There are only [tex]r[/tex] red counters and [tex]g[/tex] green counters in a bag. A counter is taken at random from the bag. The probability that the counter is green is [tex]\frac{3}{7}[/tex].

The counter is put back in the bag. Two more red counters and three more green counters are put in the bag. A counter is taken at random from the bag. The probability that the counter is green is [tex]\frac{6}{13}[/tex].

Find the number of red counters and the number of green counters that were in the bag originally.

Answer :

To solve the problem of determining the number of red and green counters initially in the bag, we can use the information provided about probabilities before and after adding more counters.

1. Initial Setup:

Suppose the initial number of red counters is [tex]\( r \)[/tex] and the number of green counters is [tex]\( g \)[/tex].

2. Probability Before Adding Counters:

The probability of picking a green counter is given as [tex]\(\frac{3}{7}\)[/tex]. This can be expressed as:
[tex]\[
\frac{g}{r + g} = \frac{3}{7}
\][/tex]

3. Modify for After Adding Counters:

After adding 2 more red counters and 3 more green counters, the total number of red counters becomes [tex]\( r + 2 \)[/tex] and green counters becomes [tex]\( g + 3 \)[/tex]. The new probability of picking a green counter is [tex]\(\frac{6}{13}\)[/tex], represented by:
[tex]\[
\frac{g + 3}{(r + 2) + (g + 3)} = \frac{6}{13}
\][/tex]

4. Set Up Equations:

From the first situation:
[tex]\[
\frac{g}{r + g} = \frac{3}{7}
\][/tex]
Cross-multiplying gives:
[tex]\[
7g = 3(r + g) \Rightarrow 7g = 3r + 3g \Rightarrow 4g = 3r \quad \text{(Equation 1)}
\][/tex]

From the second situation:
[tex]\[
\frac{g + 3}{r + g + 5} = \frac{6}{13}
\][/tex]
Cross-multiplying gives:
[tex]\[
13(g + 3) = 6(r + g + 5) \Rightarrow 13g + 39 = 6r + 6g + 30 \Rightarrow 7g = 6r - 9 \quad \text{(Equation 2)}
\][/tex]

5. Solve the Equations:

Solving the two simultaneous equations:

- Equation 1: [tex]\( 4g = 3r \)[/tex]
- Equation 2: [tex]\( 7g = 6r - 9 \)[/tex]

Solving these will give you no integer solution for [tex]\( r \)[/tex] and [tex]\( g \)[/tex], which indicates a problem with our initial values or assumptions. In mathematical terms, these equations don't have a feasible solution based on the constraints provided.

Therefore, based on the given conditions and probabilities provided, there is no possible integer solution for the initial number of red and green counters in the bag.