Sunday, January 10, 2010

How Do You Read That Decimal?

The picture above tells a thousand stories! Well, actually it might tell a tenth of a story or a hundredth of a story or a thousandth of a story depending on where the decimal point is and what digits follow the decimal point!

I cringe every time that I hear TV reporters read decimals, especially weather forecasters, because they always say things like the barometric pressure is "29 POINT 92 inches", and these guys are scientists? Yikes! I hate to think that scientists are not concerned with things like place value. 29.92 should be read as twenty-nine AND ninety-two hundredths. Maybe students do understand that 29 point 92 is almost 30, but maybe they don't. Anyway, reading decimal values using correct place value is a good place to start.


.7 is seven tenths
.70 is seventy hundreds
.700 is seven hundred thousandths

Simple, say the number like a whole number, and then say the SMALLEST place value. (and thousandths are waaaayyyyy smaller than tenths-don't believe me? ---try cutting your pizza into 1,000 equal pieces versus ten equal pieces:-} )

However, we are not limited to looking at decimal numbers and only reading them as decimals. Huh? Well, .7, .70, .700 are all also 70%, and they can all be written as fractions as well.

So, which way should we read a decimal? In short, in whatever way makes the most sense for the problem. The work above shows three ways to read each decimal, percent or fraction. If I was trying to enter 1/8 on a cheap calculator, I probably would have to use .125. If I wanted to describe the same quantity to a person, I would probably say 12 1/2%, as I have learned that most folks have a pretty good "percent schema". If I was trying to add 1/8 to a simple fraction like 1/4, I'd leave both as fractions (1/8 + 2/8 = 3/8 woohooo).

So, for a fifth grader what is important to know?

.5 or .50 or the decimal way to say 1/2
So, .675 = 67 1/2 hundredths or 67 1/2 % or 67.5 %
.33333333 is the decimal way to say 1/3
.66666666 is the decimal way to say 2/3
1 whole = 100% 2 wholes = 200% .....
So, 3 1/2 = 350% or 3.5

Be flexible, and remember that the word POINT is dead and buried!