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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.
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.
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