Adding and subtracting using a number line

The  exercise appears under the Early math Math Mission. This exercise has the Khan Academy user add or subtract two double-digit numbers using a number line.

Types of problems
There are two type of problem in this exercise:
 * 1) Add the numbers: This problem asks the student to select the correct method of adding two double-digit numbers using a number line. ASUNL1.png
 * 2) Subtract the numbers: This problem asks the student to select the correct method of subtracting two double-digit numbers using a number line. Screen+Shot+2015-08-19+at+10.57.49+AM.png

Strategies
The minimum requirement for this exercise is basic knowledge of place value, as the exercise might only be finding which numbers of tens and ones make a double-digit number.
 * 1) It's very easy to get both speed and accuracy badges in this exercise.