Diameter — Grade 7 Math, what it means and where it is taught
All the way across through the centre. d = 2r.
Taught in Grade 7 Math.
Where it is taught
Practise this idea
15 questions in the course bank use Diameter, in Length and Area in 2-D Figures, Plane Sections of 3-D Figures, Circles, Volume of Cylinders, Cones & Spheres, Equations of Circles. The first 8 are below; the rest are in those units.
Problem 1
Find the area of a circle with diameter 14. Use π ≈ 227.
Worked answer
154
r = 7
227 × 49 = 22 × 7 = 154
Problem 2
A square of side 10 cm has a circle of diameter 10 cm cut out. Find the remaining area. Use π ≈ 3.14.
Worked answer
21.5
Square: 100 cm2
Circle: 3.14 × 25 = 78.5 cm2
100 - 78.5 = 21.5 cm2
Problem 3
A shape is a 10 × 6 rectangle with a semicircle of diameter 6 on one end. Find its total area. Use π ≈ 3.14.
Worked answer
74.13
Rectangle: 10 × 6 = 60
Semicircle: 12 × 3.14 × 32 = 14.13
60 + 14.13 = 74.13
Problem 4
A cylinder is sliced straight down through its central axis. What shape appears?
- A circle
- A rectangle
- A triangle
- An oval
Worked answer
A rectangle
A rectangle: as tall as the cylinder and as wide as the diameter.
Problem 5
A cylinder has radius 4 cm and height 10 cm. It is cut vertically through its axis. Find the area of the cross section.
Worked answer
80
Height = 10 cm
Width = 2 × 4 = 8 cm
Area = 10 × 8 = 80 cm2
Problem 6
A circle has diameter 10. Find its radius.
Worked answer
5
10 ÷ 2 = 5
Problem 7
Find the area of a circle with diameter 14. Use π ≈ 227.
Worked answer
154
r = 7
227 × 49 = 154
Problem 8
A circular table has diameter 1.4 m. Find its area. Use π ≈ 227.
Worked answer
1.54
r = 0.7 m
227 × 0.49 = 1.54 m2