Solve the Equation: Finding the Missing Number in 9 + (?) = -1

Question

$9+(?)=-1$

00:00 Complete the missing part

00:04 The number is oriented and positive

00:07 The positive direction on the axis is to the right, so we'll take 9 to the right

00:27 This is the desired number, let's find it on the axis

00:31 Let's find its distance from the point (9)

00:36 The direction of movement is to the left (negative)

00:55 And this is the solution to the question

To know how much we need to add to the number 9 to get minus 1, we will count the number of steps between the numbers.

Also, we will pay attention to which direction we moved, if we moved right then the number is positive, if we moved left the number will be negative.

We will locate the number 9, and move left until we reach minus 1, where each step represents one whole number, as follows:

We discover that the number of steps is 10, and since we moved left, the number will be minus 10

$-10$