NCERT Solutions Class 6th Maths Chapter – 5 Understanding Elementary Shapes Exercise – 5.4

Question 1. What is the measure of

(i) A right angle?
Solution – Measure of a right angle = 90°

(ii) A straight angle?
Solution – Measure of a straight angle = 180°

Question 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 ∠B = 35°, then m ∠A > m ∠B.

Solution –

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

Question 3. Write down the measures of

(a) some acute angles
(b) some obtuse angles
(give at least two examples of each)

Solution –

(a) 23°, 89°
(b) Obtuse 91°, and 179°

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

Solution –

(a) The measure of an angle is 45⁰
(b) The measure of an angle is 120⁰
(c) The measure of an angle is 90⁰
(d) The measures of an angles are 60⁰, 90⁰ and 130⁰

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

Solution –

The measure of angle A is 40⁰
The measure of angle B is 68⁰
∠B has a large measure than ∠A

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

Solution – 

The measures of these angles are 45⁰ and 55⁰. Hence, angle shown in second figure is greater.

Question 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 ……… .

Solution –

(a) acute
(b) obtuse (if the angle is less than 1800)
(c) Straight
(d) acute
(e) an obtuse angle.

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

Solution –

(a) Measure of the angle = 40°
(b) Measure of the angle = 130°
(c) Measure of the angle = 65°
(d) Measure of the angle = 135°.

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

Solution –

(i) The angle between hour hand and minute hand of a clock at 9.00 am = 90°

(ii) The angle between the hour hand and minute hand of a clock at 1.00 p.m = 30°

(iii) The angle between the hour hand and minute hand of a clock at 6.00 p.m = 180°.

Question 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?

Solution –

The view through a magnifying will not change the angle measure.

Question 11. Measure and classify each angle-

Solution –