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.

## Pre-algebra

### Course: Pre-algebra>Unit 9

Lesson 1: Rate problems with fractions

# Rates with fractions

Sal solves an example problem with rates with fractions.

## Want to join the conversation?

• What happens if there is a fraction that's like 4 3/4??
• you change the mixed number to a improper fraction 4 3/4=19/4
• What is a reciprocal?
Is it just the reverse of something?
• The reciprocal of a fraction is it flipped. For example, the reciprocal of 1/5 is 5/1 (which is 5.)
The reciprocal of an integer, is 1 divided by the integer. For example, the reciprocal of 5 is 1/5 and the reciprocal of 98 is 1/98
• who created math and why? what did we do to deserve this?
• to answer your question, who made math? = (The Sumerians were the first civilization to create a counting system. Many scientists concur that addition, subtraction, multiplication, and division are among the oldest and most fundamental mathematical operations, having been used for more than 4,000 years.)

why does math exist? = (It gives us a way to understand patterns, to quantify relationships, and to predict the future. Math helps us understand the world — and we use the world to understand math.)

what did we do to deserve it? = (My fellow friend, we did absolutely nothing to deserve it!)

hopes this helps!
• I'm so confused...why am I dividing
• Since the question is asking "how many bottles will it take to clean the bathroom (or how many fractions of a bottle) " you need to divide the number of bottles per bathroom.
"per" just means divide.
Its like saying "I have 10 pickles and 2 jars. how many pickles will it take to fill each jar?"
simple, divide the number of pickles by the number of jars.
Except in the video, there are no pickles, and no jars. Instead, there are bottles of soap and bathrooms.
• Y-m-c-a
• What if you were to do it flipped around like bathroom/bottles could that sill work?
• No, it would not because ratios are like fractions and if we could switch numerators and denominators, 2/1 would equal 1/2, when 2 is greater than 1/2
• I am quite uncertain about this concept. I so happen to be in 4th grade, and I am not used to this type of formatting. If anyone could be so kind as to give me a bit of advice, it would be greatly appreciated.
• Actually, it's pretty much just dividing fractions.