Lesson objective: Apply an understanding of place value to explain how a number changes when ten is taken away.
This lesson provides an opportunity for students to apply their knowledge and understanding of place value to a mathematical situation. Students are asked to use examples to explain why all numbers do not end in zero after ten is taken away.
Key Concept students will use:
 We can find ten more or ten less without having to count.
Skills students will use:

their understanding of place value (Grade 1, Unit 8).

adding multiples of 10 with representations, (Grade 1, Unit 11).
 mental mathematics to find 10 more without needing to count (Grade 1, Unit 11).
Students engage in Mathematical Practice 7 (Look For and Make Use of Structure) as they notice how taking away 10 will change the tens place (by one ten) but not change the ones place.
Key vocabulary:
 one
 ones place
 subtract
 take away
 ten
 tens place
Special materials needed:
 base ten blocks (optional)
 hundred chart (optional)