Example: Add 7 hours 15 minutes 30 seconds, 9 hours 30 minutes 40 seconds, and 11 hours 40 minutes 32 seconds.
Work:
| hours | minutes | seconds |
|---|---|---|
| 7 | 15 | 30 |
| 9 | 30 | 40 |
| 11 | 40 | 32 |
| 28 | 26 | 42 |
Explanation: 32 seconds + 40 seconds + 30 seconds = 102 seconds. But, 102 seconds = 1 minute 42 seconds. Write the 42 below and carry the 1 minute. 1 minute (carried) + 15 minutes + 30 minutes + 40 minutes = 86 minutes. But, 86 minutes = 1 hour 26 minutes. Write the 26 and carry the 1 hour. 1 hour + 11 hours + 9 hours + 7 hours = 28 hours. Result = 28 hours 26 minutes 42 seconds.
Subtraction of Denominate Quantities
Example: Subtract 6 tons 12 cwt. 9 pounds 10 ounces from 15 tons 7 cwt. 13 pounds 9 ounces.
Work:
| Tons | Cwt. | Pounds | Ounces |
|---|---|---|---|
| 15 | 7 | 13 | 9 |
| 6 | 12 | 9 | 10 |
| 8 | 15 | 3 | 15 |
Explanation: (1) Place as in addition of denominate quantities. 10 ounces cannot be taken from 9 ounces, so we must take 1 pound from the 13 pounds and add it to the nine ounces. 16 ounces + 9 ounces = 25 ounces. 25 - 10 = 15. Write the 15 below.
(2) Now there are only 12 pounds left to take the 9 from. 12 - 9 = 3. Write the 3 below.