Exercise 5.4

Class 6 Mathematics Chapter 5|
Understanding Elementary Shapes | Exercise 5.4

1. What is the measure of (a) a right angle? (b) a straight angle?

Answer:

(a) 90°

(b) 180°

2. Say True or False :

(a) The measure of an acute angle < 90°.
(b) The measure of an obtuse angle < 90°.
(c) The measure of a reflex angle > 180°.
(d) The measure of one complete revolution = 360°.
(e) If m ∠A = 53° and m ∠B = 35°, then m ∠A > m ∠B.

Answer:

(a) True (b) False (c) True (d) True (e) True

3. Write down the measures of
(a) some acute angles.
(b) some obtuse angles.
(give at least two examples of each).

Answer :

(a) 50° , 75°

(b) 120°, 145°

4. Measure the angles given below using the Protractor and write down the measure.

Answer:

(a) 40°

(b) 130°

(c) 90°

(d) 60°

5. Which angle has a large measure?
First estimate and then measure.
Measure of Angle A =
Measure of Angle B =

Answer :

∠B has larger measure.

∠A = 40° and ∠B = 65°

6. From these two angles which has larger measure? Estimate and then confirm by measuring them.

Answer: Second angle has larger measure.

7. Fill in the blanks with acute, obtuse, right or straight :
(a) An angle whose measure is less than that of a right angle is______.
(b) An angle whose measure is greater than that of a right angle is ______.
(c) An angle whose measure is the sum of the measures of two right angles is _____.
(d) When the sum of the measures of two angles is that of a right angle, then
each one of them is ______.
(e) When the sum of the measures of two angles is that of a straight angle and if
one of them is acute then the other should be _______.

Answer:

(a) acute angle

(b) obtuse angle

(c) straight angle

(d) acute angle

(e) obtuse angle

8. Find the measure of the angle shown in each figure. (First estimate with your eyes and then find the actual measure with a protractor).

Answer:

(i) 30°

(ii) 120°

(iii) 60°

(iv) 150°

9. Find the angle measure between the hands of the clock in each figure :

Answer:

(i) 90° (Right angle)

(ii) 30° (Acute angle)

(iii) 180° (Straight angle)

10. Investigate In the given figure, the angle measures 30°. Look at the same figure through a magnifying glass. Does the angle becomes larger? Does the size of the angle change?

Answer: No, the measure of angle will be same.

11. Measure and classify each angle :

Answer:

Angle	Measure	Type
∠AOB	40	Acute
∠AOC	130	Obtuse
∠BOC	90	Right
∠DOC	90	Right
∠DOA	140	Obtuse
∠DOB	180	Straight