Final answer:
To subtract pounds and ounces, you must work with these units separately and convert if needed. For example, when subtracting ounces and you have fewer ounces than you are subtracting, convert 1 pound into 16 ounces. Subtract pounds from pounds and ounces from ounces to get the correct answer.
Step-by-step explanation:
To solve for subtraction involving customary units of weight, like pounds (lb) and ounces (oz), we need to work with these units separately, converting if necessary.
Subtracting Pounds and Ounces
For (a) 5lb - 2lb 5oz: Since we can't subtract 5oz from 0oz, we need to convert 1lb from the 5lb to 16oz (because 1lb = 16oz). So now we have 4lb 16oz - 2lb 5oz. Subtracting the pounds and ounces separately, we get 2lb and 11oz respectively.
For (b) 17T 23lb 3oz - 9T 20lb 9oz: First, subtract the tons (T), then the pounds, and lastly the ounces. Convert 1lb to 16oz to subtract the ounces if necessary. The answer will be the subtraction of each corresponding unit.
For (c) 68lb 13oz - 30lb 15oz: Since 13oz is less than 15oz, convert 1lb to 16oz. We then have 67lb 29oz - 30lb 15oz. Subtract first the pounds and then the ounces separately to get the result.