Let's denote the total number of counters in the bag before adding the blue counters as T.
Initially, 36% of T counters are red, and the rest, which is 100, are yellow.
So, initially, the number of yellow counters is 0.64×T.
When Jamal adds 50 blue counters, the total number of counters becomes T+50.
Now, 25% of the counters in the bag are blue, so the number of blue counters is 0.25×(T+50).
Since the total number of counters is the sum of red, yellow, and blue counters, we can write the equation:
0.36×T+0.64×T+0.25×(T+50)=T+50
Now, let's solve for T to find the initial total number of counters:
0.36T+0.64T+0.25T+12.5=T+50
Combine like terms:
1.25T+12.5=T+50
Subtract T from both sides:
0.25T+12.5=50
Subtract 12.5 from both sides:
0.25T=37.5
Divide by 0.25:
T=150
So, initially, there were 150 counters in the bag. Now we can find the number of yellow counters:
0.64×150=96
Therefore, there were initially 96 yellow counters in the bag.