Setting up proportions to solve word problems | 7th grade | Khan Academy

TL;DR

This video explains how to set up equations to solve word problems involving ratios and proportions.

Transcript

I have three word problems here. And what I want to do in this video is not solve the word problems but just set up the equation that we could solve to get the answer to the word problems. And essentially, we're going to be setting up proportions in either case. So in this first problem, we have 9 markers cost $11.50. And then they ask us, how much... Read More

Key Insights

• 🥳 Word problems involving ratios and proportions can be solved by setting up equations.
• 🥳 Two ratios are set equal to each other, with one including the known values and the other including the unknown value.
• 🙃 Cross-multiplication and flipping the sides of the equation are valid methods to solve for the unknown value.
• 🥳 Different approaches, such as considering the ratio between the numbers or the ratio between the costs, can be used to set up equations.

Questions & Answers

Q: How can you solve word problems with ratios using equations?

Word problems with ratios can be solved by setting up two ratios and equating them. The known values are used to determine the unknown value through cross-multiplication or flipping the sides of the equation.

Q: Can you provide an example of setting up a proportion to find the cost of markers?

In the example given, the ratio of the number of markers (9) to their cost ($11.50) is set equal to the ratio of the new number of markers (7) to the unknown cost (x). By cross-multiplying, you can find the cost of 7 markers.

Q: How do you determine the number of apples using ratios and proportions?

To find the number of apples, set up a ratio between the known number of apples (7) and their cost ($5). Equate this ratio to the ratio of the unknown number of apples (x) and their cost ($8). By solving the equation, you can determine the number of apples.

Q: What is the process for finding the number of eggs needed for a certain number of people in a cake recipe?

In this case, the ratio of people (5) to eggs (2) is set equal to the ratio of the new number of people (15) to the unknown number of eggs (x). By solving the proportion, you can find the number of eggs required.

Summary & Key Takeaways

• The video demonstrates how to set up proportions to solve word problems involving ratios and costs.

• It explains the process of setting up two ratios and setting them equal to each other to find the unknown value.

• Three example problems are provided, including finding the cost of markers, the number of apples, and the number of eggs.