1. **State the problem:** We need to find the time in seconds required to scan a table with 100,000,000 rows, each 200 bytes in size, given a disk transfer rate of 0.5 gigabytes per second. 2. **Calculate the total size of the table:** $$\text{Total size} = \text{number of rows} \times \text{size per row} = 100,000,000 \times 200 = 20,000,000,000 \text{ bytes}$$ 3. **Convert the disk transfer rate to bytes per second:** Since 1 gigabyte = 1,000,000,000 bytes, $$0.5 \text{ gigabytes/second} = 0.5 \times 1,000,000,000 = 500,000,000 \text{ bytes/second}$$ 4. **Calculate the time to scan the table:** $$\text{Time} = \frac{\text{Total size}}{\text{Transfer rate}} = \frac{20,000,000,000}{500,000,000}$$ 5. **Simplify the fraction:** $$\frac{20,000,000,000}{500,000,000} = \frac{\cancel{20,000,000,000}}{\cancel{500,000,000}} = 40$$ 6. **Final answer:** The table scan requires approximately **40 seconds**.