Math Problem Statement

At the park there is a pool shaped like a circle. A ring-shaped path goes around the pool. Its inner radius is 10 yd and its outer radius is 14 yd. We are going to give a new layer of coating to the path. If one gallon of coating can cover 8 yd², how many gallons of coating do we need? Note that coating comes only by the gallon, so the number of gallons must be a whole number. Use the value 3.14 for π.

Solution

We are tasked with finding how many gallons of coating are needed for a ring-shaped path around the pool. Let's break down the solution:

Step 1: Calculate the area of the ring-shaped path

The area of the ring is the difference between the area of the larger circle (outer radius) and the smaller circle (inner radius).

  • Area of a circle is given by the formula A=πr2A = \pi r^2.

    • Outer radius (routerr_{outer}) = 14 yd
    • Inner radius (rinnerr_{inner}) = 10 yd

    Aouter=π(14)2=3.14×196=615.44yd2A_{outer} = \pi (14)^2 = 3.14 \times 196 = 615.44 \, \text{yd}^2 Ainner=π(10)2=3.14×100=314yd2A_{inner} = \pi (10)^2 = 3.14 \times 100 = 314 \, \text{yd}^2

  • The area of the ring-shaped path is: Apath=AouterAinner=615.44314=301.44yd2A_{path} = A_{outer} - A_{inner} = 615.44 - 314 = 301.44 \, \text{yd}^2

Step 2: Determine the number of gallons needed

  • Each gallon of coating covers 8 yd².
  • To find the number of gallons required: Gallons needed=301.448=37.68\text{Gallons needed} = \frac{301.44}{8} = 37.68

Since the number of gallons must be a whole number, we round up to 38 gallons.

Final Answer:

You need 38 gallons of coating.


Would you like more details on any of these steps?

Here are five related questions you might find useful:

  1. How would the calculation change if the inner radius was larger?
  2. What if the coating covered only 5 yd² per gallon?
  3. How do you calculate the circumference of the inner and outer circles?
  4. How would the required coating change if the pool had a rectangular shape?
  5. Could you apply this method to calculate areas of other shapes like ellipses?

Tip: Always round up when dealing with materials that need to fully cover a surface!

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Math Problem Analysis

Mathematical Concepts

Geometry
Area of Circles
Subtraction of Areas

Formulas

Area of a circle A = πr²
Area of the ring = A_outer - A_inner
Gallons needed = Area / 8

Theorems

Area of a Circle

Suitable Grade Level

Grades 6-8