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2. without changing the volume of the can, come up with two new can des…

Question

  1. without changing the volume of the can, come up with two new can designs—a taller can and a wider can—and record their dimensions below.

table with columns: height, radius, volume. original: height 12.1 cm, radius 3.1 cm, volume 365.31 cm³. other columns have partial writing (e.g., 2.5 cm radius?)

  1. a colleague argues that doubling the radius of the can and halving the height will keep the volume the same. is this true? why or why not?
  2. meijer sells bubly water and is offering a president’s day sale on its individual cans. for the price of an original size can of bubly you can choose either:

a. a can with the same height but twice the radius or
b. a can with the same radius but twice the height
which offer is the better deal? explain.

  1. suppose you had the option of buying a can with twice the radius and twice the height for triple the price. is this a better or worse deal than either of the two options above? explain.

Explanation:

Response
Question 2 Solution:

First, recall the volume formula for a cylinder: \( V=\pi r^{2}h \). The original volume is \( V = \pi\times(3.1)^{2}\times12.1\approx365.31\space cm^{3}\).

Taller Can (Decrease Radius, Increase Height):

Let's choose a new radius, say \( r = 2.5\space cm \). We need to find \( h \) such that \( \pi r^{2}h=365.31 \).

Step 1: Rearrange the volume formula for \( h \)

\( h=\frac{V}{\pi r^{2}} \)

Step 2: Substitute \( V = 365.31 \) and \( r = 2.5 \)

\( h=\frac{365.31}{\pi\times(2.5)^{2}}\approx\frac{365.31}{19.635}\approx18.6\space cm \)

Wider Can (Increase Radius, Decrease Height):

Let's choose a new radius, say \( r = 4\space cm \). We need to find \( h \) such that \( \pi r^{2}h = 365.31 \).

Step 1: Rearrange the volume formula for \( h \)

\( h=\frac{V}{\pi r^{2}} \)

Step 2: Substitute \( V = 365.31 \) and \( r = 4 \)

\( h=\frac{365.31}{\pi\times(4)^{2}}\approx\frac{365.31}{50.265}\approx7.27\space cm \)

Filling the table:

Height12.1 cm18.6 cm7.27 cm
Volume\( 365.31\space cm^{3} \)\( 365.31\space cm^{3} \)\( 365.31\space cm^{3} \)
Question 3 Solution:

The volume of a cylinder is given by \( V=\pi r^{2}h \). Let the original radius be \( r \) and original height be \( h \), so original volume \( V_{1}=\pi r^{2}h \).

If we double the radius (\( r_{2} = 2r \)) and halve the height (\( h_{2}=\frac{h}{2} \)), the new volume \( V_{2}=\pi(2r)^{2}\times\frac{h}{2} \).

Step 1: Simplify \( V_{2} \)

\( V_{2}=\pi\times4r^{2}\times\frac{h}{2}=2\pi r^{2}h \)

Step 2: Compare \( V_{1} \) and \( V_{2} \)

We can see that \( V_{2} = 2V_{1} \), which means the volume doubles, not stays the same. So the colleague's argument is false because doubling the radius (which is squared in the volume formula) has a larger impact than halving the height.

Answer:

(Question 3):
No, it is not true. When the radius is doubled (\( r
ightarrow2r \)) and height is halved (\( h
ightarrow\frac{h}{2} \)), the new volume \( V_{new}=\pi(2r)^{2}(\frac{h}{2}) = 2\pi r^{2}h=2V_{original} \), so the volume doubles, not remains the same.

Question 4 Solution:

Let the original radius be \( r \) and original height be \( h \), so original volume \( V=\pi r^{2}h \).

Option a: Same height, twice the radius (\( r_{a}=2r \), \( h_{a}=h \))

Volume of option a: \( V_{a}=\pi(2r)^{2}h=\pi\times4r^{2}h = 4\pi r^{2}h=4V \)

Option b: Same radius, twice the height (\( r_{b}=r \), \( h_{b}=2h \))

Volume of option b: \( V_{b}=\pi r^{2}(2h)=2\pi r^{2}h = 2V \)

Since \( V_{a}=4V \) and \( V_{b}=2V \), and both cost the same as the original can (which has volume \( V \)), option a gives a larger volume (4 times the original) compared to option b (2 times the original). So option a is a better deal.