The cost of a certain metal varies directly as its weight increases. If 6 ounces cost $9 , how much will 15 ounces cost ?

Question

Direct variation equations

Answer 1

Let's find the price per ounce!

6 ounces costs $9, so the price for each ounce is

($9)/(6 oz) = 1.5 $/oz

Now we can find how much 15 ounces will cost by multiplying the cost per ounce by the number ounces we want.

(1.5 $/oz)*(15 oz) = $22.50.

Let me know if that makes sense, and if you have any other questions feel free to shoot me a direct message!

-Ethan

Answer 2

Hello!

The key to solving this exercise is find the constant of proportionality (let's call it k) associated with weight to cost.

For example, if 6 ounces cost $9, then we can write 6k = 9. This means that k = 9/6 = 3/2.

Next, we can write 15k = 15(3/2) = 45/2 = 22.5. This means that 15 ounces cost $22.50.

Let me know if you have any questions.