Addition and subtraction: Complete the missing numbers

To find out which number is missing, we solve the entire exercise to know which number we will have to add to obtain a result of 25:

$9+3=12$

To make 12 equal to 25 we will have to add the number 13.

Let's verify:

$25-12=13$

To find out which number is missing, we solve the entire exercise to know which number we will have to add to obtain a result of 20:

$7+2=9$

To make 9 equal to 20 we will have to add the number 11.

Let's verify:

$20-9=11$

To find out which number is missing, we solve the entire exercise to know which number we will have to add to get a result of 25:

$9-3=6$

To make 6 equal to 25 we will have to add 19.

Let's verify:

$25-6=19$

The question mark is the unknown, so we will refer to the exercise as an equation.

We arrange the exercise to isolate the question mark:

$17+4-?=5$

We reduce:

$21-?=5$

We move to thevariable to the other side and change to the correct sign:

$21=?+5$

We move the 5 to the other side and change to the correct sign: $21-5=\text{?}$

$16=\text{?}$

To find out which number is missing, we solve the entire exercise to know which number we will have to add to obtain a result of 29:

$12+3-1=$

$15-1=14$

To make 14 equal to 29, we will have to add 15.

Let's verify:

$29-14=15$