A mixture of 150 liters contains 20% Diesel (the rest is Petrol). How many more liters of Diesel must be added so that Diesel becomes 25% of the new mixture?

Introduction / Context:
We increase the Diesel component by adding pure Diesel. The Diesel amount changes while Petrol stays the same; total volume also increases by the added Diesel.

Given Data / Assumptions:

• Initial total = 150 L; Diesel = 20% = 30 L; Petrol = 120 L.
• Add y liters Diesel.
• Target Diesel% = 25%.

Concept / Approach:
Set (Diesel after addition)/(Total after addition) = 25% and solve for y.

Step-by-Step Solution:
(30 + y) / (150 + y) = 0.2530 + y = 37.5 + 0.25y ⇒ 0.75y = 7.5 ⇒ y = 10 L

Verification / Alternative check:
New total = 160 L; Diesel = 40 L; 40/160 = 0.25 = 25%.

Why Other Options Are Wrong:
5, 15, 20, 35 produce Diesel percentages different from 25%.

Common Pitfalls:
Using 25% of the original total or forgetting that the denominator changes after adding Diesel.

Final Answer:
10 liter