Solve the Equation: Finding the Unknown in 12-?=15

Question

Solve the following problem:

$12-?=15$

00:00 Find the unknown

00:03 Find point (12) on the axis

00:07 Find the desired result (15) on the axis

00:12 Find the number of jumps between the result and starting point

00:17 We can see that the difference is +3

00:26 Negative times negative always equals positive

00:30 Therefore we subtract by (-3)

00:37 And this is the solution to the question

We know that the distance between 12 and 15 is three steps.

In other words:

$12+3=15$

Now let's remember the rule:

$-(-x)=+$

We'll substitute x with the number 3 as follows:

$12-(-3)=15$

Therefore, the answer is minus 3

$-3$