1.NBT.C.6
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.
Unpacked
This standard is foundational for future work in subtraction with more complex numbers.
Students should have multiple experiences representing numbers that are multiples of 10
(e.g. 90) with models or drawings. Then they subtract multiples of 10 (e.g. 20) using
these representations or strategies based on place value. These opportunities develop
fluency of addition and subtraction facts and reinforce counting up and back by 10s.
Examples:



70 - 30: Seven 10s take away three 10s is four 10s
80 - 50: 80, 70 (one 10), 60 (two 10s), 50 (three 10s), 40 (four 10s), 30 (five 10s)
60-40: I know that 4+2 is 6 so four 10s + two10s is six 10s so 60-40 is 20
Students may use interactive versions of models (base ten blocks, 100s charts, number
lines, etc.) to demonstrate and justify their thinking.
First Grade students use concrete models, drawings and place value strategies to subtract
multiples of 10 from decade numbers (e.g., 30, 40, 50).
Example: There are 60 students in the gym. 30 students leave. How many students
are still in the gym?
See the five different strategies below:
Student 3
I used a number line. I started at 60 and moved back 3 jumps of 10 and landed on 30.
There are 30 students left.
Student 4
I used ten frames. I had 6 ten frames- that’s 60. I removed three ten frames because 30
students left the gym. There are 30 students left in the gym.
Student 5
I thought, “30 and what makes 60?. I know 3 and 3 is 6. So, I thought that 30 and 30
makes 60. There are 30 students still in the gym.
30
+
30
=
60
Note: This standard in no way addresses using an algorithm to solve. It specifically
states: 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. The strategies
above demonstrate what this should look like at this point in time.
Speaking
Level 2
Emerging
Describe how
to subtract
multiples of
10 in the
range of 1090 by
explaining
strategies
using their
native
language to
fill in gaps
while
working with
a partner.
Level 3
Developing
Describe how
to subtract
multiples of
10 in the
range of 1090 by
discussing
the strategies
in a small
group.
Level 4
Expanding
Describe
how to
subtract
multiples of
10 in the
range of 1090 by
discussing
the
strategies
and
reasoning in
a small
group and
by using
complete
sentences.
Level 5
Bridging
Describe how
to subtract
multiples of
10 in the
range of 1090 by
discussing
the strategies
and
reasoning
independentl
y and by
using
complete
sentences.
ELD Standard #3: English Language Learners communicate information, ideas,
and concepts necessary for academic success in the content area of
Mathematics.
Level 6 Reaching
Level 1
Entering
Describe
how to
subtract
multiples of
10 in the
range of 1090 by
explaining
strategies in
their native
language
while
working with
teacher
support.