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paul's calculator can make only two operations :
add 12 to the number displayed ,or subtract 7 from it.
today, it shows the number 1998.
what is the minimal number of steps needed to display the number 2000?
The resulting increase from repeating the two operations = +2
Let x = no. of +12 steps
Let y = no. of -7 steps
12x - 7y = 2
-7y = -12x + 2
7y = 12x - 2; multiplied by -1
Substitute values for x until you get an integer value for y
x = 6 ea +12 steps
y = 10 ea -7 steps
Total 16 steps