Answer:
1382.3 cm²
Step-by-step explanation:
We'll assume that we have to find the total surface area, including the areas of the ends.
The area of the side is given by A = 2πr·h and that of each of the ends by A = πr².
Thus, the side area is A = 2π·(10 cm)·(12 cm) = 240π cm² ≅ 754.0 cm²
and double the area of the base is A = 2·π·(10 cm)² = 628.3 cm²
and so the total surface area of the can (including the ends) is 1382.3 cm²
Answer: ![4r + 5(20-r) \le 92](https://tex.z-dn.net/?f=4r%20%2B%205%2820-r%29%20%5Cle%2092)
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Explanation:
r = number of red pens
4r = cost of buying r red pens
example: if r = 10, then 4r = 4*10 = 40 is the total cost of buying 10 red pens
If John buys r red pens, then he must buy 20-r black pens so that r and 20-r add to 20.
John buys 20-r black pens, and at $5 each, so it will cost 5(20-r) dollars for just the black pens alone.
In total, John spends 4r + 5(20-r) dollars for all the pens (red & black)
We want $92 be the most he spends. This is the ceiling or highest value possible.
Therefore,
![4r + 5(20-r) \le 92](https://tex.z-dn.net/?f=4r%20%2B%205%2820-r%29%20%5Cle%2092)
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Extra info:
If you want to solve for r, then
![4r + 5(20-r) \le 92](https://tex.z-dn.net/?f=4r%20%2B%205%2820-r%29%20%5Cle%2092)
distribute
![100 - r \le 92](https://tex.z-dn.net/?f=100%20-%20r%20%5Cle%2092)
add r to both sides
![100 \le 92+r](https://tex.z-dn.net/?f=100%20%5Cle%2092%2Br)
subtract 92 from both sides
![8 \le r](https://tex.z-dn.net/?f=8%20%5Cle%20r)
![r \ge 8](https://tex.z-dn.net/?f=r%20%5Cge%208)
So John must buy at least 8 red pens. The most he can buy is 20 red pens since he wants 20 pens total.
It's B Rotation I believe