Compare Decimals Using Like Units
Comparing decimals by rewriting them to the same number of decimal places — like units — makes comparison as straightforward as comparing whole numbers, as taught in Grade 4 Pengi Math. Adding trailing zeros (e.g., 0.5 becomes 0.50) does not change the decimal’s value but makes the place values align for direct comparison. Once both decimals have the same number of digits, compare them as if they were integers. This approach eliminates the common mistake of thinking longer decimals are automatically larger.
Key Concepts
To compare decimals, rewrite them so they have the same number of decimal places (like units) by adding trailing zeros. This does not change the decimal's value. Once in like units, compare the numbers as if they were whole numbers.
Common Questions
How do you compare decimals using like units?
Add trailing zeros to give both decimals the same number of decimal places, then compare them as whole numbers. Example: 0.4 vs. 0.37 → 0.40 vs. 0.37 → 40 > 37, so 0.4 > 0.37.
Does adding a trailing zero change a decimal’s value?
No. 0.5 = 0.50 = 0.500. Adding trailing zeros after the last non-zero digit only changes the written form, not the value.
Why is 0.4 greater than 0.37 even though 0.37 has more digits?
0.4 = 0.40 = 40 hundredths. 0.37 = 37 hundredths. 40 hundredths > 37 hundredths. More decimal digits does not mean a larger value.
What are ‘like units’ in decimal comparison?
Like units means all compared decimals are expressed in the same place value denomination (e.g., all in hundredths). It’s the decimal equivalent of having a common denominator.
How does comparing decimals by like units help avoid mistakes?
Students often think 0.37 > 0.4 because 37 > 4. Converting to like units (hundredths) shows 0.37 = 37 hundredths and 0.40 = 40 hundredths, making the correct comparison obvious.