Subtract tens

The first instance of the Subtract tens exercise is under the Early Math Math Mission. This exercise helps students to see division as an undoing of addition. It also continues to solidify understanding of numbers as groups of tens.

Types of problems
There are two types of problems that show up in this exercise:
 * 1) Subtraction in groups of ten: This problem begins with a subtraction question with two multiples of ten. It then goes step-by-step through a process of breaking the subtraction problem into groups of tens. The student is asked to fill in an answer at each step and eventually arrives at a final answer.Sub1.png
 * 2) Subtraction as missing addition: This problem begins with a fill in the blank addition problem. It then uses the same set of numbers and changes the problem into a corresponding subtraction problem.Sub2.png

Strategies
These problems go quickly making this exercise fairly easy to attain both speed and accuracy badges.


 * 1) On the second problem type, the two answers for the two slots will always be the same 2-digit number since it is trying to encourage the connection between addition and subtraction.