Suppose you need to add two numbers together?
Once again, your answer is only as accurate as the LEAST ACCURATE of the numbers you added to get it.
For instance, let's look at our woman who weighs 120 pounds.
She puts on a pair of jeans that weighs about 1 lb, a pair of shoes that weigh about 1.5 lb, and a sweater that weighs about half a pound. What will the scale read when she steps on it again?
120 + 1 + 1.5 + .5 = ?
And you're right! Remember, you didn't know whether she really weighed 120 lbs, or whether she was just rounding it to the nearest ten pounds. So if she adds about 3 pounds of clothing, do you really know much more about her weight?
Also, you don't know if her jeans really weigh a pound, or if she's rounding that to the nearest pound.
Sad, isn't it? But it's fair.
YOU CAN'T MAKE BAD DATA INTO GOOD DATA BY ADDING MORE DATA.
all clip art from Microsoft