Anonymous

mom we have a cheater!

Anonymous

Sometimes there isn't such a need. AND you cannot add apples and oranges. You can add apples to apples. You can add feet to feet. But you cannot make any sense of trying to add liters to gallons. That's like trying to add blue and red together to get green. It doesn't work.

Anonymous

Quantities in science describe things in the real world. They aren't just numbers, they are numbers of units. There is a difference between 3 inches and 3 kilometers, or between 10 grams and 10 pounds. Whatever math you do with those numbers, you need to keep track of the units. 2 meters plus 3 centimeters is 2.03 meters; you can't just add 2 + 3 and say the answer is 5 inches. And if you're ever trying to add 2 meters plus 3 gallons, you've probably made a mistake. Often you need a unit to cancel out in order to make your answer meaningful. Driving 10 meters per second for 2 hours will take you 20 meter-hours per second, but it's a lot easier to understand that distance if I describe it as 72 kilometers.

Anonymous

no need

Anonymous

Utilizing the units is one technique that solves many problems! Here's some examples: