Regrouping when subtracting one-digit numbers

The  exercise appears under the Early math Math Mission. This exercise has the Khan Academy user subtracting a single digit number from a double digit number using regrouping (carrying).

Types of problems
There is one type of problem in this exercise:
 * 1) Regroup to sutract: This type of problem has the user subtract a one-digit number from a two-digit number using regrouping (carrying). RWSODN.png

Strategies
Basic knowledge of subtraction and regrouping is required for this exercise.
 * 1) It's easy to get accuracy badges in this exercise.

Real-life Applications
These types of more complicated subtracting are likely to come up more often in the real world.
 * 1) Money usually deals with adding and subtracting 1-3 digit numbers.