Area/Perimeter Of Combined or Partial Shapes

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Area/Perimeter Of Combined or Partial
Shapes
• The trick to calculating the area or perimeter
of a combined or partial shape is to divide up
the figure into shapes for which you can find
the area and perimeter.
Area/Perimeter Of Combined or Partial
Shapes
Using the dotted lines to
divide the shape into 3
rectangles allows you to
use the dimensions you
are given and the formula
for the area of a rectangle
to find the areas of the 3
sections. Add those 3 areas
together to find the area of the entire figure. For perimeter, add
up all the outside side lengths of the figure.
The large rectangle: A = (4 + 10 + 4) 12
= 18  12
= 216 sq. units
The small rectangles (same size): A = 10  4
= 40 sq. units (each)
Area of total figure: A = 216 + 40 + 40
= 296 sq. units
Perimeter:
Start at the top and add all the side lengths.
P = 10 + 4 + 4 + 12 + 4 + 4 + 10 + 4 + 4 +12 + 4 + 4
= 76 units
• Can you find the area and perimeter of this
figure?
• Can you find the area
and perimeter of this figure?
For the area, we have a rectangle attached to
half of a circle. We’ll need to find the area of
each and then add them together.
• The area of a rectangle
formula is: A = LW
A = 5x10
A = 50
The area of a circle formula
is: A = πr2
The circle’s diameter is 10, so the radius is 5.
A = 3.14 x 52
A = 3.14 x 25
A = 78.5
We only have half of a circle,
so the area of the semi-circle
is one half of 78.5.
Area of semicircle 39.25
Area of rectangle 50
Total area of shape 50 + 39.25 = 89.25
How would you calculate the
perimeter of this shape?
How would you calculate the
perimeter of this shape?
Again, we have the rectangular part, which is
straight forward, but we also need to figure
out the semi-circle part.
Circumference is perimeter for circles. We’ll use
that formula to find the circumference if this
was a whole circle. Half of that will be the
distance around the semi-circle.
Circumference of the whole circle:
C = πD
C= 3.14 x 10
= 31.4 units
Circumference of the semi-circle:
31.4 ÷ 2 = 15.7 units
Perimeter of the total figure:
P = 20 + 15.7
= 35.7
Area/Perimeter Of Combined or Partial
Shapes
• Try the problems on the bottom of page 161
through page 162 in the book. Check your
answers online.
• Do the GED Practice problems on pages 27
and 28 in the packet, and enter your answers
online.

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