Scientific Notation Online Practice

To determine which pair of numbers shows that the second number is an estimation of the first, we should look for pairs where the second number rounds to or approximates the first number.

Let's analyze each pair:

1. **0.00345; 0.004** - The second number (0.004) is a rounded form of the first number (0.00345).

2. **0.00345; 0.003** - The second number (0.003) is not a close estimation of the first number (0.00345).

3. **345; 400** - The second number (400) is an estimation of the first number (345) if we round 345 to the nearest hundred.

4. **275; 200** - The second number (200) does not closely estimate the first number (275).

Based on this analysis, both the pairs **0.00345; 0.004** and **345; 400** show the second number as an estimation of the first. However, since we typically seek the closest estimation, the first pair is the most straightforward.

**Answer:** 0.00345; 0.004