## Multi-digit by One-digit Multiplication

When developing multi-digit by one-digit multiplication, it is important to stress place value so students will have a solid foundation when they learn the multiplication algorithm. Materials: Overhead projector or chalkboard. Preparation: Write

 4 2 x 3
on the board or overhead projector.

• Ask: How many tens are in 42? How many ones are in 42? What is 42 in expanded form?
The first two questions should be easy for students. There are 4 tens and 2 ones in 42. Some students may need help with the third question. Elicit from them that 4 tens equal 40 and 2 ones equal 2, so the expanded form of 42 is 40 + 2. Write 40 + 2 times 3 on the board next to 42 times 3.

 4 2 x 3
 40 + 2 x 3

• Say: We'll multiply the ones first. What is 2 times 3?
Students should know their multiplication facts well enough to promptly say 6.

• Say: What is 40 times 3? Students should have sufficient experience with multiplying by multiples of ten to know the answer is 120.

• Write 120 + 6 on the board below 40 + 2 times 3.
 4 2 x 3
 40 + 2 x 3
120  +  6

• Say: Now we just have to find the sum of 120 + 6. What is the sum?