The Commutative property: Worded problems

A hardware factory that manufactured screws for one entire week.

Every day there were 300 screws manufactured.

On the second day, 14 screws were defective and and had to be thrown away.

Similarly, on the fourth day 7 screws were thrown away, and on the fifth day 26 screws were thrown away.

How many good screws were manufactured that week?

First, we calculate how many screws the factory produces in total in 7 days:

$7\times300=2100$

Now we subtract the number of defective screws that we know the factory discarded on the second day:

$2100-14=2086$

Now let's count the number of defective screws that we know the factory discarded on the fourth day:

$2086-7=2079$

Now we record the number of defective screws that we know the factory discarded on the fifth day:

$2079-26=2053$

2053

Teacher Ana brought 5 cakes to class.

Teachers Silvia and Monica also brought cakes and tripled the number of cakes.

Each cake was divided into 12 slices.

How many students could eat cake if each student eats one slice?

First, we find how many cakes there are in total.

Let's pay attention to the phrase: "Silvia and Monica tripled the number of cakes"

That is, if Ana brings 5 cakes, then now there are:

$5\times3=15$

Now we find the number of slices.

If each cake is divided into 12 slicesand there are a total of 15 cakes, then:

$15\times12=180$

180 total slices. In other words, enough for 180 students.

180

Damian is training for a race.

The first day he ran 3.4 km..

The second day he ran round trip for 1.18 km..

On the third day Damian ran 2.6 km...

How many kilometers in total did Damian run during the three days of training?

Let's consider the number of kilometers Damian ran each day

On the second day it is written "round trip", that is, twice.

Therefore, we write the following exercise:

$3.4+2\times1.18+2.6=$

We solve the multiplication exercise:

$3.4+2.36+2.6=$

We arrange the exercise using the commutative property, to make it more convenient to solve:

$3.4+2.6+2.36=$

We solve the exercise from left to right:

$3.4+2.6=6$

$6+2.36=8.36$

8.36