Why is duralumin used for the manufacture of automobiles and speed boats ?

Explanation

### Step-by-Step Solution:

1. **Identify the Material**: Duralumin is an alloy primarily made of aluminum, which is known for its lightweight properties.

**Hint**: Think about what materials are commonly used in vehicles and their properties.

2. **Lightweight Nature**: Duralumin is very light, which is crucial for automobiles and speedboats. A lighter vehicle can achieve better fuel efficiency and speed.

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