Circles: word problems

Learning Objectives Identify the radius and diameter of a circle from a word problem. Select the appropriate formula (circumference or area) to solve a given word problem involving circles. Calculate the circumference of a circle given its radius or diameter in a word problem context. Calculate the area of a circle given its radius or diameter in a word problem context. Solve multi-step word problems involving both circumference and area of circles. Use the approximation of $\pi$ (e.g., 3.14 or 22/7) correctly in calculations. Interpret and apply units of measurement correctly in circle word problems. Have you ever wondered how much frosting you need for a round cake, or how far a bicycle wheel travels in one spin? 🎂🚴‍♀️ We'll learn how to solve these kinds of puzzl...

TermDefinitionExample CircleA round shape where all points on the boundary are the same distance from the center.A hula hoop or a coin are examples of circles. Radius (r)The distance from the center of a circle to any point on its edge.If a pizza is cut into slices, the length of the crust from the center to the edge of one slice is the radius. Diameter (d)The distance across a circle passing through its center. It's twice the radius.The length of a straight line going from one side of a circular clock face, through the middle, to the other side is the diameter. Circumference (C)The distance around the outside of a circle.If you walk around the edge of a circular pond, the total distance you walk is the circumference. Area (A)The amount of surface inside a circle.The amount of grass...

Diameter from Radius $d = 2r$ Use this rule to find the diameter if you are given the radius, or vice versa. The diameter is always twice the radius. Circumference of a Circle $C = \pi d$ or $C = 2\pi r$ Use this formula to find the distance around a circle. Use $\pi d$ if you know the diameter, or $2\pi r$ if you know the radius. Remember, circumference is measured in linear units (e.g., cm, m). Area of a Circle $A = \pi r^2$ Use this formula to find the amount of space inside a circle. You must use the radius ($r$) for this formula. If given the diameter, first find the radius ($r = d/2$). Area is measured in square units (e.g., cm$^2$, m$^2$).