The number 21 is in a lot of places. If you are a gambler, you may think of 21 at a blackjack table. In the game, you start out with being dealt two cards. One card is face-up for everyone to see. The other card is face down. Only you can see that card.

Face cards are worth 10 points. Aces are worth either 1 or 11. You get to decide on that one. The other cards are worth the amount that is on the card. Your goal is to get to 21 or closest without going over.

Once you go over 21, you would lose…unless you bluff. Now, at this point with your two cards, you can get more cards, one at a time. At any point, you can stop if you think you might go over 21. Look at the two cards below.

Do you know how you could get a perfect blackjack amount of 21? The seven card is face up for everyone to see. This would require for you to know the factors of 21.

Factors of 21 are 1, 3, 7, and 21

Look at the images below. They show two groupings. These have to do with the factors of 21.

This image shows several game pieces. Each set of game pieces has 3 in it. Then there are 7 groups. So, the factors for 21 are 3 and 7. It can also be grouped the other way around.

This also shows the factors of 21.

Now, back to our blackjack game. You have a seven. How could you get a perfect blackjack score of 21 with your other two cards? This has to do with the other two cards. We know that 3 groups of 7 equals 21, and so each of the other two cards would need to be sevens.

Therefore, we know that the factors of 21 are 3 and 7. However, 1 and 21 are also factors of 21. All of the factors would be 1, 3, 7, and 21.

Challenging Questions

Pretend you are 21 years old. You are writing a book about your life. However, you want to have 3 chapters for your book. How many years will be included in each chapter if you want to spread your life among your chapters evenly? So, each chapter will include the same amount of years from your life.

Answer

In this case, there would be 7 years of your life for each chapter. One way to do this would be to have your early childhood to be the first 7 years of your life. Your middle childhood would include the next 7 years from 7 to 14. Then the last chapter would include the last part of your childhood. It would be 14 to 21 years old.

You may have been to a military funeral before. If not, be aware that one thing they do is called a 21-gun salute. This means that there are 21 guns shoot in the air. If they shoot at one time, explain how many guns do the shooting by using the factors of 21?

Answer

This may seem like an obvious answer to a question. However, to prove that 21 guns would be going off at one time, you could show that two factors of 21 are 1 and itself. This is true for all numbers. So, if the guns are going off at one time, this factor’s partner would be the amount of guns. Number 1’s partner is 21.

Let’s say that you, unfortunately, have 21 days left to pay a bill. You get paid each week which is 7 days. How many times will you pay by the time you get to the 21st day? Use the factors of 21 to answer the question.

Answer

There are 4 factors for the number 21. Divide 21 by 7. This would give you the answer of 3. So, you would make 3 payments by the 21st of the month. To use factors, look at the factor partner for 7. In other words what number times seven equals 21? It would be 3. With factors, each factor has a partner. Now, sometimes, the factor number and its partner are the same number.

Frequently Asked Questions

Usually, when you have a higher number, there are many factors because you have a higher number. However, in this case, 21 only has a few factors. One reason is because it is an odd number. Even numbers always have a factor of 2 because it is an even number. In this case, 21 only has 4 factors. Like all other numbers, it has 1 and itself, 21, are always factors. However, there is only one other set of numbers that can evenly be divided into 21 without having a remainder.

Sometimes, it is difficult to find all of the factors for a number. There is no way to know immediately with a number how many factors belong to that number, unless you memorized them. So, in this case, it might confuse people that there are only 4 factors for 21. Being an odd number, some people may not pick up the only two other factors than 1 and itself.

Most students use factoring with things or objects that come in groups of 21. There are many things that come in groups of 21. Obviously, the birthday of 21 is a very important number. There is a 21-gun salute. There is no such thing as a 20-gun or 22-gun salute. In these cases, you would use 21 only. To answer or figure out questions, you may need to use the factors of 21. Unless 3 or 7 is included and things are grouped, most likely you would have a remainder. Other things that come in groups of 21 are days, weeks, and a popular gambling game like blackjack.