Maryland Math 1.NOS.E.12

1.NOS.E.12 is a cluster heading. These are the individual standards under it.

• 1.NOS.E.12.a

  Use concrete models or drawings to subtract.

• 1.NOS.E.12.b

  Use counting strategies, properties of operations, and/or the inverse relationship between addition and subtraction to subtract.

• 1.NOS.E.12.c

  Represent and explain the calculation by connecting the strategy used to the meaning of subtraction.

01

What Students Need to Do

Students subtract tens from tens up to 90. They use bundles of ten, drawings, or counting back by tens to show what they take away and what remains.

02

What Mastery Looks Like

For 80 − 30, a student draws eight groups of ten, crosses out three, and writes 50. They explain that five groups of ten remain and check that 50 + 30 = 80.

03

Common Misconceptions

Some students subtract the tens digits and write 5 instead of 50 for 80 − 30. Others count back three ones instead of three tens, or cross out the wrong number of groups.

04

How to Assess It

Exit ticket: Solve 70 − 40 with a tens drawing. Cross out the groups you remove, write the answer, and explain what remains.

1. 01

   Give pairs nine bundles of ten craft sticks; ask them to model 90 − 40 and say how many tens remain.

2. 02

   Show two drawings for 60 − 20, one crossing out two tens and one crossing out two dots; ask which fits and why.

3. 03

   Play tens-card match: students pair subtraction cards, such as 80 − 30, with answer cards and justify each match by counting back tens.

4. 04

   Set out eight boxes labeled 10 pencils each; remove three boxes and have students record how many pencils are left.

• 2.NOS.C.9

  Add and subtract within 1000, recognizing that when adding or subtracting three-digit numbers, one adds or subtracts hundreds and hundreds, tens and tens, ones ...

• 1.NOS.E.13

  Subtract a 1-digit number from a 2-digit number (without regrouping).