Solving Proportions 03:28 minutes

Video Transcript

Transcript Solving Proportions

Andretti the Yeti is worried. Why's he worried? Well, in two hours, he has a date with Nettie the Bodacious Yeti and it's just started to snow.

Snow? What's a little snow when you have a date with the love of your life? Well, Rule #5 of the Yeti Handbook states, if the snow is four feet deep, you can't be outside. Andretti doesn’t know if he'll be able to make it to her place.

The Yeti Weatherman reports the snow will fall at a constant rate of one foot of snow per half hour for the next several hours. Nettie is expecting him in 2 hours. In two hours, will the height of the snow be less than four feet?

Setting up a Proportion or two equal Ratios

Let’s help him figure this out! We can set up a proportion, also known as two equal ratios. Ratios compare quantities. When you set up a proportion, the numerators and denominators of each ratio must contain the same variable.

Our proportion will contain ratios comparing the amount of snow in feet per hour. Let's look at the given information. We know it's snowing one foot per half hour. How deep will the snow be in two hours?

Solving Example Proportion

Andretti the Yeti has an idea of how to solve this problem. He left us a hint in the snow. To solve for the unknown quantity of snow, we'll use cross multiplication, also known as cross product.

Don't confuse cross multiplication with cross cancellation. You use cross cancellation to make multiplying fractions easier.

Set the two cross products equal to each other. 1 · 2 = 2 and 0.5 · f = 0.5f. We are left with 2 = 0.5f.

To solve, divide both sides by 0.5. f = 4. At this rate, in two hours the snow will be four feet deep. Oh no! That won't work. What should Andretti do?

Example Proportion 2

He should then plan to arrive earlier for his date! He doesn't want to break the Yeti rule, so he needs to get there before the snow is 4 feet deep. In how many hours will the snow be only three and one-half feet deep?

Using the same ratio, let’s set up another proportion, this time to solve for the unknown quantity of hours. We will solve this proportion just like we did before, using cross multiplication.

h = 0.5 · 3.5. To get to Nettie’s place before the snow is too deep, Andretti should plan to meet with her in 1.75 hours, or an hour and three-quarters. He needs to leave fifteen minutes earlier than originally planned.

Nettie is finally ready for their date. Poor Andretti, he followed Yeti Rule number 7 and waited outside of her house since he was too early.

1 comment
  1. Julia redaktion

    One of my favorite videos!

    Posted by Julia Feistel, over 2 years ago