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Fractions intro

# Intro to fractions

Sal divides wholes into equal-sized pieces to create unit fractions. Created by Sal Khan.

## Want to join the conversation?

• how do we simplify :

(5a)^3 divided by 5a ^-1 x 5^-2 a^2
• The first thing I like to do is multiply everything out and make all the exponents positive, just so that we can get an idea of what we're working with. You can distribute the exponents to each factor that it's raising:
125a^3 / 5^-1 * a^-1 * 5^-2 * a^2

Now that we have everything all laid out, let's make all the exponents positive, just to simplify the problem a bit more:
= 125a^3 * 5^1 * a^1 * 5^2 / a^2
= 5^3 * 5 * 5^2 * a^3 * a / a^2

Now we can combine the exponents, keeping in mind the rule for doing so:
x^a * x^b = x^(a+b)
x^a / x^b = x^(a-b)

5^(3+1+2) * a^(3+1-2)
= 5^6 * a^2

This means that the final answer is 15,625a^2
• At , why did they use the shapes a rectangle and a square?
• Since both squares and rectangles have congruent (similar) sides, then they can be easily cut into integer (whole number) pieces that make it easier to understand in terms of the overall lesson.
• Hi, this isn't about the video, but is it possible to see a lesson about probability somewhere? I would like to know what or means in probability.
• Why do fractions help us in life?
• well, fractions are very usefull. take money. i need to pay my bill of \$100 by the end of the month. i have \$35 so far. so i have 35/100 of what i need.
(1 vote)
• Hii! um...how do you divide fractions? also i think it is very fun to multiply fractions so may u please make a video on that? Thank you!
• to multiply fractions, simply multiply the numerators, and put that over the product of the denominators. For example, lets say we have 1/5*2/3, 1(2) = 2 and 5(3) = 15, so you get 2/15, and when you divide fractions, you simply take the recipricol of the dividend and then multiply.
• Go me+smart group!
• It looks like the triangle that Sal show last could be divided into 8 equal parts. I think the top of the red colored triangle starts at the middle of the side of the big triangle. So the small triangle would be 1/8 of the larger triangle. Anyone agree?
• Is the triangle 1/6 equal part? If not, what is it? I'd like to know what part of the triangle was shaded and how it was derived. I'll have a hard time sleeping until I understand how to figure out what fractional part of that triangle was shaded.