SME
Grade 3 Math · Number & Base Ten
Fluently add and subtract within 1,000
Use this for “Find 245 + 138,” and to check a take-away by adding back.
Diagram
Flats are hundreds, rods are tens, small cubes are ones.
This is an example. Type your own values to start a new problem.
First number
+
Second number
=
Total
Formulas
245 + 138 = 383
First number + second number = total
Assumptions
•
Line up hundreds, tens and ones. Add or take away one place at a time, starting with the ones.
•
Trade 10 ones for 1 ten, or 10 tens for 1 hundred, when a place gets past 9.
•
Check a take-away by adding back: 383 − 138 = 245, and 245 + 138 = 383.
Step-by-step
WE KNOW
First number: 245
Second number: 138
FIND
total
Step 1 · Find total
245 + 138 = ?
First number + second number = total
Add the ones, then the tens, then the hundreds. Trade 10 for 1 of the next place.
1
2
4
5
+
1
3
8
3
8
3
Ones: 5 + 8 = 13
Tens: 40 + 30 = 70
Hundreds: 200 + 100 = 300
Total = 383
Check
Put the numbers back in. Both sides should match.
245 + 138 = 383 ✓
Topic check
See what you know: 5 questions on this topic
New questions each time. Pass to mark it complete.