How to multiply three or more numbers

Students find the product of three factors by multiplying in two steps.

• Step A, then step B: 19 × 32 = 608, then 608 × 15 = 9,120
• Choose an easy pair first: 152 × 5 = 760, then 760 × 10
• Multiply by tens and hundreds: 150 × 20 × 10 = 30,000
• Check large products against three choices, up to 26,486,000

Grouping factors in any order uses the associative property, 3.OA.B.5; the multi-digit steps are 5.NBT.B.5.

Print page one and read the worked example in the orange box together: 12 × 9 = 108, then 108 × 33.

• Before starting, ask which two factors are easiest to multiply first.
• Write the step A result at the top of step B.
• For the tick boxes, work the product out fully, then compare.

The second half stacks three factors in one column; treat it the same way, two at a time. Page two shows steps A and B for each guided product.

• Multiplying only two factors: 1,470 × 10 = 14,700 is half done; it still needs × 45.
• Losing zeros: 410 × 200 × 323 is 26,486,000, while 2,648,000 drops a zero.
• Adding instead of multiplying the step A result in step B.

Next, use the same steps in word problems with three or more numbers, such as trays, rows and sandwiches.