"Question 4 Rukhsar painted the outside of the cabinet of measure 1 m × 2 m × 1.5 m. How much surface area did she cover if she painted all except the bottom of the cabinet?
Class 8 Mensuration Page 186"
Answers
b=1m
h=1.5m
Surface area of the cabinet=2(lb + lh + bh)
=2(2 x 1 + 2 x 1.5 + 1 x 1.5)
=2(2 + 3 + 1.5)
=2(6.5)
=13
Painted surface area=13 - 2 = 11 sq cm
Mensuration:
Mensuration is the branch of mathematics which concerns itself with the measurement of Lengths, areas & volume of different geometrical shapes or figures.
Surface area:
The surface area of a solid is the sum of the areas of the plane or curved faces of the solid.
It is measured in square units such as square centimetre (cm²) and square metre (m²).
Surface area of cuboid is the sum of the surface areas of its six rectangular faces.
Surface Area of Cuboid is =2(lb + lh + bh)
By surface area of a cuboid we mean the total surface area.
The sum of the areas of 4 vertical faces of a cuboid is called its lateral surface area.
The lateral surface area or the area of the four walls of the cuboid .
Area of the four walls = 2 (l +b) h
==========================================================
Solution:
Given:
Length of cabinet(l) = 2 m, Breadth of(b) = 1 m
Height of cabinet (h)= 1.5 m
Surface area of cabinet= area of top + lateral surface area
= lb + 2(l+b)h
Surface area of cabinet= lb + 2(l+b)h
= 2×1+2(2+1)×1.5
= 2+2(3)× 1.5
= 2+ 6 ×1.5
= 2+ 9
= 11 m²
Hence, the required surface area of cabinet is 11m²
=========================================================
Hope this will help you...