1st Grade · Number & Operations in Base Ten
1.NBT.B.2: Understand that the two digits of a two-digit number represent amounts of tens and ones
1.NBT.B.2 is a 1st grade Common Core math standard in Number & Operations in Base Ten. Here’s what it really covers, and how you can help your students learn it.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
The standard
Understand that the two digits of a two-digit number represent amounts of tens and ones. Understand the following as special cases: a. 10 can be thought of as a bundle of ten ones called a "ten." b. The numbers from 11 to 19 are composed of a ten and one, two, three, four, five, six, seven, eight, or nine ones. c. The numbers 10, 20, 30, 40, 50, 60, 70, 80, 90 refer to one, two, three, four, five, six, seven, eight, or nine tens (and 0 ones).
In plain words
Understand that the two digits of a two-digit number represent amounts of tens and ones.
Sample questions from student practice
These questions from Bobby's Math Club are the kinds of questions your students will see. You can try answering them to see what a student might see.
Question 1 of 3
What number is 3 tens and 4 ones?
- 43
- 34
- 7
Where students can get stuck
- Reading the 3 in 34 as three ones, so showing 34 with sticks means putting out 3 sticks and 4 sticks.
- Seeing 14 as one number to count up to, rather than as a ten and 4 ones.
- Treating the zero in 60 as nothing, so reading or writing 60 as 6.
Effective teaching strategies
- Show 34 with 3 ten rods and 4 ones cubes, and ask what the 3 and the 4 each count, so students see the 3 stands for three tens.
- Build 14 by snapping 10 cubes into a stick and adding 4 single cubes, so students see a ten and 4 ones rather than a count up to 14.
- Ask students to build 60 with six ten rods and no ones, then explain what the 0 is doing and what the number would mean without it.
Units that teach this standard
Find where 1.NBT.B.2 lands in the program you teach. Each unit has a guide written for families. Unit names and order vary between editions and districts, so your school’s own materials have the exact sequence.
Bridges in Mathematics
enVision Mathematics
Eureka Math
Everyday Mathematics
i-Ready Classroom Mathematics
Illustrative Mathematics
Math Expressions
Reveal Math
Don’t see your curriculum? Contact Bobby and we’ll see if we can help!
Share it with families
Families can read Tens and ones in two-digit numbers for a plain-language look at this skill, with three questions to try together and ideas for helping at home.
Help every student practice place value at home
In Bobby's Math Club, students practice at just the right level, with a hint when they need one, a clear explanation after every question, and kid-friendly videos. Unlimited practice is free for every family.
See how it works for teachers
Written by Robert “Bobby” Barnett
Bobby is an award-winning math teacher, the author of Meet Every Learner’s Needs, and the father of two elementary-school math learners. He uses Bobby’s Math Club with his own kids a few times every week. Learn more or contact Bobby.