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### Unit 4: Lesson 3

Compare and interpret constants of proportionality

# Interpret proportionality constants

Sal interpret what the constant of proportionality means in a context.

## Want to join the conversation?

• at i don't understand why the answer isn't answer B. Can anyone help? •  It's SImple! `d = 2c` where `d` stands for `dollar` and `c` stands for `cupcake`.

Let's say we were given the value where `c = 1` and we had to find `d`, this means that we have to find the price of one cupcake. So let's substitute the value in the formula.
` d = 2(1) = 2` or it can also be written as `d = 2 * 1 = 2`
This also means that for each cupcake we are charged 2 dollars!

Remember `2c` in the formula doesn't mean 2 cupcakes. It's that the cupcakes are just being multiplied by 2

Hope you got it! Feel free to ask if you have any doubts!
• I'm still really confused :/ • This whole concept confuses me. If d=2c, and if d is dollars, and c is cupcakes, the equation directly reads dollar equals two cupcake, which means that one dollar equals two cupcakes, so I should get two cupcakes for one dollar. Even if I divide d by two, I get d/2=c, and if I divide a dollar by two, I get 50 cents equals one cupcake. I just don't understand how Sal got the answer that it is two dollars per cupcake. I saw his formula but the formula doesn't make sense. Can someone please help? • bruh this is mad confusing. • how would h equal 1/5 • It took me a while to understand this, too. I was reading the equation as a very direct statement instead of solving for d, which is probably what you are doing, too. Here's a breakdown:

d=5h
This seems like 1 of d (1 cm) is equal to 5 of h (5 hours), right? But that's not solving for d - that's assigning a value of 1 to d and then interpreting it as a statement rather than an equation.

d=5h

d (whatever this number is) is the equivalent of 5 of h. So, if h has a value of 1 (one hour), then to get the value of d, we have to multiply the value of h by 5. We are not saying literally 5 hours - we are saying the value of the depth in cm is the equivalent of 5 times the value of h.

So let's give h a value of 1, because each of h is a single hour. That means the equation reads like this: d = 5 x 1. This means the ratio of d to h is 5:1, or that the value of h is 1/5 that of d.

I hope this helps!
• All of this makes sense to me, but has anyone encountered the euro/dollar question in practice? I can't figure out how to solve it.

For those who haven't seen it, e (euro) = 17/20 d (dollar)

They then ask how many euros we need for one dollar, and vice versa.

I don't even know where to start... someone explain? • How does this work with fractions? • but b kinda makes sense because you can sell cupcakes for a dollar which makes it more difficult and confusing to just pick A for some of ya saying "oh A dosn't makes sense" i know i said it to not putting any words into any bodys mouth just saying not confusing you just saying what comes to mind   