 ## Grade 1 Math: Subtraction 11-20

In this lesson, students learn to identify equivalent forms of the same number. The sum of any two numbers is an equivalent form of those numbers.

In the problems in this lesson, students are given a number and they select an addition statement that represents an equivalent number.

### Subtraction 11-20: No Regrouping

In this lesson students learn how to subtract a single digit number from a two-digit number from 11 through 20, when no regrouping is required. The subtraction process is illustrated by decomposing the two digit number into 10 and some number of ones. These ones are then subtracted and the result added to 10 to get the difference of the two original numbers.

### Subtraction 11-20: Regrouping

In this lesson students learn how to subtract a single digit number from a two-digit number from 11 through 20, when regrouping is required. The process is the inverse of the “make a ten” strategy which requires decomposing a ten, or “breaking a ten.” The minuend is first decomposed into the sum of ten and some number of ones. The subtrahend is then subtracted from ten. The result of this subtraction is then added to the number of ones in the minuend. The result is the difference.

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