Multiply one-digit whole numbers by multiples of 10 in the range 10-90 (e.g., 9 × 80, 5 × 60) using strategies based on place value and properties of operations.
Official wording from the Common Core State Standards for Mathematics (© 2010 National Governors Association Center for Best Practices and Council of Chief State School Officers). View on thecorestandards.org
What is 9 × 80? Third graders reason that 80 is 8 tens, so 9 × 80 is 9 × 8 tens, which is 72 tens, or 720. This standard covers products of a one-digit number and a multiple of 10 from 10 to 90, and the goal is understanding why the answer works rather than a rule about "adding a zero."
Two properties carry the reasoning. Place value says 80 = 8 × 10, and the associative property lets students regroup: 9 × (8 × 10) = (9 × 8) × 10 = 72 × 10. Base-ten blocks make this visible: 9 groups of 8 ten-rods is 72 ten-rods, and 72 tens is 720. Once students see this, they can multiply quickly while still knowing what the digits mean, which matters later when the same thinking extends to 400 × 6, 30 × 50 and decimals, where the "add a zero" shortcut breaks down completely. Products in this standard reach as high as 810, so students also practise reading three-digit numbers in tens.
Students taught only this rule may write 5 × 60 = 3000 by counting zeros carelessly, or later apply it to decimals. Keep asking how many tens the product is.
For 5 × 40, a child may write 20 tens as 20 and stop, or write 2000. The fact 5 × 4 = 20 already ends in zero, and 20 tens is 200.
Some students compute 6 × 30 as 6 × 3 = 18 and forget the product is in tens. Label the answer: 18 tens = 180.
Students may think 4 × 10 is 14. Revisit equal groups: 4 groups of 10 is 40.
Find 9 × 80 and explain using place value.
Answer: 9 × 80 = 720 because 9 groups of 8 tens make 72 tens.
Use ten-rods or bundles of 10 straws so students physically make groups of tens. Recording sentences such as "4 × 3 tens = 12 tens = 120" keeps the place value visible. Connect to skip counting by tens and to the hundreds chart.
Test items commonly ask for the product, for an equivalent expression like (3 × 7) × 10, or for a word problem answer. This standard sets up 4.NBT.B.5, where students multiply multi-digit numbers using place value.
Original questions written for this standard. Choose an option or type your answer, then press Check. Every question has a worked explanation.
Answer: 300
60 is 6 tens. 5 × 6 tens = 30 tens = 300.
Answer: 280
7 × 4 tens = 28 tens = 280.
Answer: D) (6 × 3) × 10
30 = 3 × 10, so 6 × 30 = (6 × 3) × 10 = 18 × 10 = 180.
Answer: A) 400
8 × 5 tens = 40 tens = 400. The fact 8 × 5 already ends in zero.
Answer: 180 (also accepted: 180 apples)
9 × 2 tens = 18 tens = 180 apples.
Answer: C) 28 tens
4 × 7 tens = 28 tens, which is 280.
Understand that the three digits of a three-digit number represent amounts of hundreds, tens, and ones; e.g., 706 equals 7 hundreds, 0 tens, and 6 ones. Understand the following as special cases:
A full lesson with slides, activities and an exit ticket on multiplying by multiples of 10, pitched to grade 3 and editable in PowerPoint or Google Slides.
Make a lesson →A printable, differentiated worksheet on 3.NBT.A.3 with an answer key, ready in about a minute.
Make a worksheet →Turn multiplying by multiples of 10 into a quiz students answer online that marks itself, with a class summary for you.
Build a test →One-digit whole numbers multiplied by multiples of 10 from 10 to 90, such as 9 × 80 or 5 × 60.
The standard asks students to use strategies based on place value and properties of operations. A pattern is fine once understood, but students should explain that the product is a number of tens.