-- A diameter is any straight line inside the circle that goes through the center and touches the curvy part twice.
-- Every diameter of the same circle has the same length.
-- The distance around every circle is (its diameter) multiplied by (pi).
-- Half of the diameter is called the "radius" of the circle. A radius is any straight line inside the circle that goes between the center and the curvy part.
-- The area of every circle is (its radius, squared) times (pi).
-- 'Pi' ( π ) is a number. It's a decimal that keeps going forever and never ends, so you can never write it exactly with numbers.
-- Pi is roughly 3.14 , and if you use 3.14 whenever you need pi, then your answers will be about 0.05% too small.
That's very close. When you turn in an answer that's only 0.05% wrong, the teacher knows that you know how to solve the problem, and that's way more important than the answer.
For the circle in your picture, the diameter is 17in, the radius is 8.5in, and the area must be (pi) (8.5)² square inches. You can go ahead and work that out.
David can read 50 pages in 50 minutes. (50 pages)/(50 minutes) = 1 page/minute Since David reads 1 page per minute, in 80 minutes David can read 80 pages.
