Cogito
Grade 2 Math · Chapter 3 · Lesson 6
What Zero Means
A 0 holds a place open. It does not mean nothing is there.
10 problems · about 12 minutes · 2.NBT.A.1, 2.NBT.A.3
What this lesson teaches
The child interprets a zero digit as "none of that unit" and keeps the other places correct.
- A 0 means none of that unit, not nothing at all.
- The 0 holds the other digits in their places.
- 204 and 24 are completely different numbers.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Three Ways to Write a Number: 400 + 70 + 5 in digits?
Answer 475
Why 400 + 70 + 5 = 475.
Review — Counting to 1,000: What comes after 499?
Answer 500
Why After 499 comes 500.
Warm Up
Straightforward practice. Get the method working first.
4 problems7 hundreds, 0 tens and 2 ones is which number?
Answer 702
Why It is 702.
Why must the 0 in 204 be written?
Answer It keeps the 2 in the hundreds place.
Why Without the 0 the number becomes 24.
4 hundreds, 0 tens, 9 ones is which number?
Answer 409
Why Do not skip the tens column.
In 807, how many tens are there?
Answer 0
Why Look at the middle digit.
Build It Up
The same ideas with more to keep track of.
2 problemsIn 610, how many ones are there?
Answer 0
Why Look at the last digit.
What does the 0 in 305 mean?
Answer There are no tens.
Why There are still 3 hundreds and 5 ones.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Careless Answer: 3 hundreds, 0 tens and 6 ones. What is the number?
Answer 306
Why It is 306. Writing 36 would lose the hundreds.
No Ones: 5 hundreds, 7 tens and 0 ones. What is the number?
Answer 570
Why It is 570.