Model multiplication with money
Model Multiplication with Money in Grade 4 Saxon Math Intermediate 4 uses physical bills to make two-digit multiplication concrete. For 14 x 3, students lay out three groups of one 10-dollar bill and four 1-dollar bills. Counting yields three 10s and twelve 1s. They then regroup: exchange ten 1-dollar bills for one 10-dollar bill, leaving two 1s and four 10s total, giving 42 dollars. For 26 x 4, students count 8 ten-dollar bills and 24 one-dollar bills, regroup 24 ones into two additional 10s plus four 1s, and reach a final answer of 104 dollars. This method makes regrouping visual and intuitive.
Key Concepts
Property To show multiplication like $14 \times 3$ with money, you lay out the amount multiple times. For this problem, you would create three groups of money, with each group containing one 10 dollars bill and four 1 dollars bills. This gives you a hands on way to see all the parts before you combine them and regroup.
Example For $14 \times 3$, you start with three 10 dollars bills and twelve 1 dollars bills. Then, you exchange ten of the 1 dollars bills for one 10 dollars bill. You are left with four 10 dollars bills and two 1 dollars bills, which equals 42 dollars.
Explanation It’s like being a banker! You gather all the bills, but you can't have a giant pile of one dollars bills. You exchange every ten 1 dollars bills for a new 10 dollars bill, then count up your neat stacks.
Common Questions
How does the money model work for multiplication?
Lay out the dollar amount once for each factor. Count all bills of the same denomination, then regroup ten 1-dollar bills for one 10-dollar bill. Count the final stacks to get the answer.
How do you model 14 x 3 with money?
Make three groups of one 10-dollar bill and four 1-dollar bills. You have 3 tens and 12 ones. Exchange 10 ones for one 10: now 4 tens and 2 ones = 42 dollars.
How do you model 26 x 4 with money?
Make four groups of two 10-dollar bills and six 1-dollar bills: 8 tens and 24 ones. Exchange 20 ones for two 10s: 10 tens and 4 ones = 104 dollars.
Why does the money model help with regrouping?
It makes the abstract process of carrying visible. Trading ten 1-dollar bills for one 10-dollar bill is exactly what carrying in written multiplication does.
What is the most common mistake when multiplying with regrouping?
Forgetting to add the regrouped (carried) tens after multiplying the tens digit. Always add the carry before recording the tens digit of the answer.