Balance Balls

Step 1: Analyze the first two scales   

 From the first scale, we can establish the relationship between the balls:   

𝐴=𝐶+𝐵+𝐷

 From the second scale, we can establish another relationship:   

𝐶=𝐵+𝐷

 Step 2: Substitute the value of C into the first equation          

A=(B+D)+B+D

A=2B+2D

 Step 3: Analyze the third scale and solve for the value of B   

 The third scale shows that one red ball (A) is equal to three blue balls (D).   

𝐴=3𝐷

 Substitute this into the equation from Step 2:   

3D=2B+2D

 Subtract

2𝐷

 from both sides:   

Final Answer is 𝐷=2𝐵

Meaning that a blue ball (D) is equal to two yellow balls (B).