Preparing for class 8 final exams and stuck with a tricky question? Don’t panic! For your benefit, our Maths subject experts have meticulously prepared a list of important questions for CBSE class 8 Math chapter-wise and topic-wise.
Important questions based on NCERT syllabus for Class 7 Class 8 Chapter 11 - Mensuration:
Question 1: The radii of two circles are 49 cm and 63 cm. How much longer is the circumference of the second circle than the first?
Circumference of first circle = 2πr = 2π × 49 = 308 cm
Circumference of second circle = 2πr = 2π × 63 = 396 cm
Subtracting the circumference of the circle with a smaller radius from the circle with a bigger radius we have 396 - 308 = 88 cms
So, the second circle is longer than the first circle by 88 cms.
Question 2: In a building there are 24 cylindrical pillars. The radius of each pillar is 28 cm and height is 4 m. Find the total cost of painting the curved surface area of all pillars at the rate of 8 per m^2.
Radius of cylindrical pillar, r = 28 cm = 0.28 m
Height, h = 4 m
Curved surface area of a cylinder = 2πrh
Curved surface area of a pillar = 2 × 22/7 × 0.28 × 4 = 7.04 m^2.
Curved surface area of 24 such pillar = 7.04 × 24 = 168.96 m^2.
Cost of painting an area of 1 m^2 = Rs.8
Therefore, cost of painting 168.96 m^2
= 168.96 × 8 = Rs.1351.68
Question 3: Find the perimeters and area of the parallelograms given in figure.
=2×(l+b) = 2×(10+6) cm = 32 cm
Area=Base × Corresponding altitude
=(10×5) cm^2 = 50 cm^2
=2×(l+b) = 2×(9+5) cm = 28 cm
Area=Base × corresponding altitude
= (5×8) cm^2 [Base = 5 cm as opposite sides of a parallelogram are equal]
= 40 cm^2