Question

Total surface area of a cuboid having dimensions l*b*h is __________

(a) l*b*h

(b) 2(lb + bh + lh)

(c) lb + bh + lh

(d) 6l^2

This question was posed to me by my college professor while I was bunking the class.

Origin of the question is Surface Areas and Volumes in portion Surface Areas and Volumes of Mathematics – Class 9

Answer 1

Correct choice is (b) 2(lb + bh + lh)

Explanation: As shown in the figure below,

The total surface area of a cuboid is the sum of the area of six rectangles constituting the cuboid.

The six rectangles forms three pairs of rectangles (which are at opposite sides) who have the same surface area.

Area of one pair of rectangles having sides l and b = 2(l*b)

Area of the second pair of rectangle having sides b and h = 2(b*h)

Area of the third pair of rectangle having sides l and h = 2(l*h)

The total area of the cuboid = sum of three pairs of rectangles

= 2(l*b) + 2(b*h) + 2(l*h)

= 2(lb + bh + lh).