Multiplying Using Unit Form
Grade 4 Eureka Math students multiply multiples of ten by thinking in unit form. Instead of treating 50 × 30 as a large computation, they see it as 5 tens times 3 tens = 15 hundreds = 1,500. The rule is: multiply the non-zero digits, then multiply the place value units. For 40 × 20, compute 4 × 2 = 8, then tens × tens = hundreds, giving 800. This mental math strategy leverages place value understanding and lays the foundation for the area model and partial products multiplication.
Key Concepts
To multiply numbers in unit form, multiply the digits and then multiply the place value units. $$(a \text{ tens}) \times (b \text{ tens}) = (a \times b) \text{ hundreds}$$ $$(a \text{ tens}) \times (b \text{ ones}) = (a \times b) \text{ tens}$$.
Common Questions
How do you multiply using unit form?
Express each factor in unit form (e.g., 50 = 5 tens). Multiply the digits first, then multiply the units (tens × tens = hundreds).
What is 50 times 30 in unit form?
5 tens times 3 tens = 15 hundreds = 1,500.
What is 40 times 20 using this strategy?
4 tens times 2 tens = 8 hundreds = 800.
What place value unit do you get when multiplying tens by tens?
Tens multiplied by tens gives hundreds, because 10 × 10 = 100.
How does unit-form multiplication connect to the area model?
In the area model, multiplying tens by tens produces the hundreds partial product, which is one rectangle in the model.