An alloy of copper and bronze weight 50g. It contains 80% Copper. How much copper should be added to the alloy so that percentage of copper is increased to 90%?

Step 1: Understand the given values

• Total weight of the alloy = 50g
• Percentage of copper = 80%
• Copper content = 80% of 50g = (80 / 100) × 50 = 40g
• We need to add more pure copper to raise the copper content to 90% in the new alloy.

Step 2: Let the amount of copper to be added be x grams.

So, new total weight of the mixture = 50g + x

New copper content = 40g (original) + x

Step 3: Set up the equation based on final percentage:

(40 + x) / (50 + x) = 90 / 100

Step 4: Solve the equation

(40 + x) / (50 + x) = 9 / 10

Cross-multiply:
10(40 + x) = 9(50 + x)
400 + 10x = 450 + 9x

Now, subtract 9x from both sides:
400 + x = 450

Now subtract 400 from both sides:
x = 50

Answer: 50 grams

To increase the copper content from 80% to 90%, we must add 50 grams of pure copper.

This type of alloy problem is common in competitive exams like SSC, banking, and school-level aptitude tests. The key is to set up the right proportion based on percentage composition. Using equations and solving step-by-step makes the logic clear for learners.