Being able to add, subtract, multiply and divide numbers by memory and in your head is one of the most important skills you will ever have.

Today you will be working on memorizing 13 - a number (0 to 19).

Good Luck with your assignment.

Warning in matrix(as.vector(string_m), ncol = 2): data length [21] is not a
sub-multiple or multiple of the number of rows [11]

                               
 11 - 0 = 11       11 - 11 = 0 
 11 - 1 = 10       11 - 12 = -1
 11 - 2 = 9        11 - 13 = -2
 11 - 3 = 8        11 - 14 = -3
 11 - 4 = 7        11 - 15 = -4
 11 - 5 = 6        11 - 16 = -5
 11 - 6 = 5        11 - 17 = -6
 11 - 7 = 4        11 - 18 = -7
 11 - 8 = 3        11 - 19 = -8
 11 - 9 = 2        11 - 20 = -9
 11 - 10 = 1       11 - 0 = 11 

On the following pages there will be one problem per page. The page following the problem will have a solution. The goal is to maximize accuracy and speed.

100 problems will appear in total. See if you can identify the answer accurately and measure how long it takes to get through all 100.

Nice Job! Keep up the good work and remember to always have fun while you are learning.