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Topic _

_

Area of Triangles [2] (Lesson 11)

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Tutor: _

Topic:

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T_OPIC NAME

Primary 5: Rev Up! Math

Recap:

Area of a triangle is _ × base of triangle × height of triangle

A BC

The base of triangle FBD is

Line FD.

The height that is

D corresponding to its base is

F E Line BE which is

perpendicular to Line FED. It

has the same length as line CD

(breadth of rectangle ACDF.

1 cm C D

1 cm

height

A base B

(a) Area of Triangle ABC is .

(b) Area of Triangle ABD is .

Therefore, we can conclude that triangles with bases and

equal heights have the areas.

1

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Primary 5: Rev Up! Math

Exercise 1: Finding the area of figures made up of rectangles, squares and

triangles.

1. The figures below show 4 identical rectangles.

Which two of the shaded triangles have the same area?

A B CD

Ans: Triangles and .

2. Find the area of triangle ABC as shown below.

C

2 cm

A B

2 cm

Ans: 2

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Primary 5: Rev Up! Math

3. In the figure, ABCDE is made up of square ABDE and triangle BCD.

ED = DC = 6 cm. Find the area of the figure.

AB

6 cm

ED C

Ans:

4. ABCE is a rectangle 14 cm by 7 cm. ED = 4 cm

Find the area of the shaded region ABDE.

A 14 cm B

7 cm

E 4 cm D C

Ans: 3

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Primary 5: Rev Up! Math

5. ABCD is a rectangle. EC = 3cm.

a) What is the area of triangle BDE?

b) What is the area of the unshaded region?

A 11 cm D

6 cm

B E 3cm C

Ans: a)

b)

6. In the figure, BD = 12 m. Find the area of figure ABCD.

9m

12 m 7m

Ans: 4

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Primary 5: Rev Up! Math

7. The figure is made up of a triangle and a square.

The perimeter of the figure is 28 cm.

Find the area of the triangle.

5 cm 5 cm

4cm

Ans:

8.. Find the area of the unshaded part of the figure shown below.

7 cm

20 cm

30 cm

Ans: 5

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Primary 5: Rev Up! Math

*9. Find the area of the shaded triangle.

8 cm

Ans:

*10. The figure, ABFG and CDEF are squares. AEF is a triangle.

GF = 28 cm and FE = 20 cm.

a) Find the area of triangle AEF.

b) Find the area of the shaded region.

AB

CD

G FE

28 cm 20 cm

Ans: a) 6

b)

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Mini Test Primary 5: Rev Up! Math

1) Find the area of triangle ABD. A

7 cm

9 cm

D B 6 cm C

8 cm Ans:

2) In the figure PQRST, QT = 6 cm, QS = 8 cm and TS = 10 cm. R

Find the area of rectangle PRST.

Q 8 cm S

P

6 cm

10 cm

T C

Ans: 8 cm

D

3) In the figure, ACDE is a rectangle of length 22 cm by 8 cm.

AF = FE and AB = BC, Find the shaded area. 7

AB

=

F

=

E 22 cm

Ans:

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Primary 5: Rev Up! Math

Extension

1) ABCD is a rectangle. AE = ED and DF = FC.

What is the area of the shaded triangle?

A 18 cm B

=

E 16 cm

=

DFC

Ans:

2) In the figure, ABFG and CDEF are squares and BDG is a triangle. GD is a straight

line. GF = 16 cm and FE = 21 cm. Find the area of the shaded triangle BDG.

CD

AB

GF E

16 cm

21 cm

Ans: 8

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