If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Lesson 5: Fractions with denominators of 10 and 100

# Adding fractions (denominators 10 & 100)

Sal adds 3/10+7/100 by finding a common denominator. Created by Sal Khan.

## Want to join the conversation?

• but what if the numerator is bigger the denomanator? I mean like 16/10 + 6/100
• If your comparing numbers like 7/14 and 14/7 try multiplying the denominators into the same number, then multiply the numerator with the same amount that you multiplied for the denominator.For 7/14 you will get 28/28 and for 14/7 you will get 28/28.Then you see which numerator is bigger if none are then they are equivalent.
• hey whats the denominator again
• the one on the bottom.
• ok so this did help me and let me understand a little bit when the person doing the voice over is making it a little harder to ya know, understand? all im asking is for them to explain a TINY bit more... thankyou and hope you understand...
• Okay! Let's get a different situation. 7/10 + 4/100=?. We need to find out the sum. The first thing we need to do is that we need to make the denominators the same. We have to make the denominators 100, because you cannot divide 4 by 10 without decimals. So we times 10 by 10=100. Then we have to times the numerator by 10 too! 7x10=70. It becomes 4/100+70/100+?. Now, 70+4=74 so, the answer is 74/100. Hope this helps and have a good day!
• is that the only way you can add fractions or?
• When adding fractions, you always need to have a common denominator. So, yes. The process shown in the video are the steps you would need to take.
• What is the variable of 5a
• A variable is a letter that represents an unknown number. A variable can be any letter so it would mean the same thing if it said 5s . so in your case a is the variable
• Do I have to use a number line?
• No you just have to figure out what it's going to equal times our added I don't get it completely either
• GCD means Greatest Common Factor right?
• Actually, "greatest common denominator" does not make good sense since because a common denominator can be as large as one likes. (For example, if the denominators of two fractions are 4 and 6, then the numbers 12, 24, 36, 48, 60, and so on forever are all common denominators!)
GCD actually means greatest common divisor, which means the same thing as GCF (greatest common factor) because a divisor of a number means the same thing as a factor of a number. For example, the GCD of 4 and 6 is the GCF of 4 and 6, which is 2.
Have a blessed, wonderful day!
• why does he do 10 times 10 at ? I don't get it.
• In order to add or subtract a fraction, each fraction must have the same denominator (bottom number). This is done by multiplying one or both of the fractions by a number that will change the denominator, but not the value of the fraction as a whole. So, in the video he is attempting to add 3/10 and 7/100. He can't do so since they have different denominators, so he multiplies 3/10 by 10/10 (any number over itself is equal to 1) and obtains the necessary denominator of 100, but it also changes his numerator as well, leaving him with 30/100. In the video he was just referencing the denominators alone at that mark because the denominator is the most important aspect of adding and subtracting fractions.

Hope this helped!