Math trick

This is the line math trick;

It is very simple, all you have to do is with the first number, which is 4. Draw 4 lines and leave a little space and then draw 2 more lines for the 2. Then draw 1 line going the opposite way for the 1 and 3 lines with a little space in between. Count the lines in groups like above seperated by the green line. Left, right and middle; then theres your answer.