jmc

The amount in quarters is $20\times 25$ cents and the total amount is $50\times 10+20\times 25$ cents. The percent of the value in quarters is $$\frac{20\times 25}{50\times 10+20\times 25}=\frac{500}{500+500}=\frac{500}{1000}=\boxed{50\%}.$$