The decimal point
A point that shows where the units end.
Is 42 enough?
A pencil is 4 units and 2 tenths long. Could we just write its length as 42?
Is “42” enough to show 4 units and 2 tenths?
What this lesson covers
The idea
A point, called the decimal point, is used as a separator to show where the whole number part ends and the fractional part starts; without it the same digits could stand for different quantities.
Is 42 enough?
A pencil is 4 units and 2 tenths long. Could we just write its length as 42?
Is “42” enough to show 4 units and 2 tenths?
- Yes, 42 is fine
- No, it could mean something else too
- Yes, if we write the unit next to it
Move the point
The digits 7 0 5 never change. Slide the decimal point and see what each digit stands for.
A point that separates
The same digits 7 0 5 can stand for three different quantities. The decimal point shows where the whole number part ends.
A point, called the decimal point, shows where the whole number part ends and the fractional part starts. Without it, the same digits could stand for different quantities.
- Written | Meaning
- 705 | 7 hundreds and 5 ones
- 70.5 | 7 tens and 5 tenths
- 7.05 | 7 ones and 5 hundredths
Notes
The decimal point shows where the whole number part ends and the fractional part starts. Without it, the same digits can mean different quantities.
Check yourself
In 70.5, what does the digit 5 stand for?
A pencil is 4 units and 2 tenths long. How do we write it?
In 70.5, the part before the decimal point is a whole number. Which one?
Answer: 70
70 is the whole number part; 5 tenths is the fractional part.
Which number has the digit 3 in the tenths place?
- 5 ones. The ones place is just before the point. The 5 is after it.
- 5 tenths — correct. Yes! It comes right after the point, so it is in the tenths place.
- 5 tens. The 5 is on the right of the point, so it is smaller than ones.
- 0.42. That is 4 tenths and 2 hundredths. The 4 should be units.
- 4.2 — correct. Yes! 4 units, the point, then 2 tenths.
- 42. That is 4 tens and 2 ones. We need the point after the 4.
- 0.35 — correct. Yes! The first place after the point is tenths, and it holds the 3.
- 0.53. Here the 3 is in the second place after the point: hundredths.
- 3.5. Here the 3 is before the point, in the ones place.