1st Grade · Number & Operations in Base Ten
1.NBT.C.6: Subtract multiples of 10 in the range 10-90
1.NBT.C.6 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
Subtract multiples of 10 in the range 10-90 from multiples of 10 in the range 10-90 (positive or zero differences), using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used.
In plain words
Subtract multiples of 10 in the range 10-90.
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 is 60 minus 20?
- 40
- 50
- 80
Where students can get stuck
- Forgetting the zero, writing 4 instead of 40 as the answer to 70 - 30.
- Counting back by ones from 70, thirty separate times, instead of counting back by tens: 60, 50, 40.
- Answering 1 instead of 10 for 60 - 50, losing track of the fact that the answer is still in tens.
Effective teaching strategies
- Count back by tens from 70 with ten rods, removing one rod at a time and saying 60, 50, 40, to find 70 − 30.
- Ask students to say each problem in tens, such as 7 tens minus 3 tens leaves 4 tens, and then write the answer as 40.
- Give 60 − 50 and ask students to use ten rods to explain why the answer is 10 and not 1, since one ten remains.
Watch our video
A short, kid-friendly lesson on this skill, for the whole class or for students to watch on their own.
Units that teach this standard
Find where 1.NBT.C.6 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
Don’t see your curriculum? Contact Bobby and we’ll see if we can help!
Share it with families
Families can read Subtracting tens, like 70 - 30 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.