Three measurements are made as 18.425 cm, 7.21 cm and 5.00 cm. The addition should be written as

Options

A. 30.635 cm
B. 30.64 cm
C. 30.63 cm
D. 30.6 cm

Answer

To solve the problem of adding the three measurements (18.425 cm, 7.21 cm, and 5.00 cm) and expressing the result with the correct number of significant figures, follow these steps:

### Step-by-Step Solution:

1. **List the Measurements**:
- First measurement: 18.425 cm
- Second measurement: 7.21 cm
- Third measurement: 5.00 cm

2. **Perform the Addition**:
- Add the three measurements together:
\[ 18.425 + 7.21 + 5.00 = 30.635 \text{ cm} \]

3. **Determine the Least Number of Decimal Places**:
- Look at the decimal places of each measurement:
- 18.425 has 3 decimal places.
- 7.21 has 2 decimal places.
- 5.00 has 2 decimal places.
- The least number of decimal places among these measurements is 2 (from 7.21 and 5.00).

4. **Round the Result**:
- Since the result (30.635 cm) needs to be rounded to 2 decimal places:
- The first two decimal places of 30.635 are 63.
- The third decimal place is 5, which means we need to round up.
- The number preceding the 5 (which is 3) is odd, so we add 1 to it.
- Therefore, 3 becomes 4.

5. **Final Result**:
- The final result, rounded to 2 decimal places, is:
\[ 30.64 \text{ cm} \]

### Final Answer:
The addition should be written as **30.64 cm**.