surface AREAS and Volumes
213
1. A plastic box 1.5 m long, 1.2
EXERCISE 13.1
stic box 1.5 m long, 1.25 m wide and 65 cm deep is to be made. It is opened at the
lgnoring the thickness of the plastic sheet, determine:
The area of the sheet required for making the box.
(1)
G)
The cost of sheet for it, it a sheet measuring Im costs Rs 20.
Answers
Length, l = 1.5m
Breadth, b = 1.25m
Height, h = 65cm = 0.65m
CSA: curved surface area of cuboid = 2(l+b)h = 2 * (1.50+1.25) * 0.65 = 3.575m^2
Area of base = lb = 1.5 * 1.25 = 1.875m^2
(i) Therefore, total area = 3.575 + 1.875 = 5.45m^2
Cost of plastic sheet= Rs.20/m^2
(ii) Therefore total cost of making the box = 5.45 * 20 = Rs.109
Question :-
A plastic box 1.5 m long, 1.25 m wide and 65 cm deep is to be made. It is opened at the top. Ignoring the thickness of the plastic sheet, determine
(i) The area of the sheet required for making the box.
(ii) The cost of sheet for it, if a sheet measuring 1m2 costs ₹20.
Answer :-
(i) Here, length (l) = 1.5 m, bread th(b) = 1 .25 m
and height (h) = 65 cm = 65/100 m = 0.65 m
∵ It is open from the top.
∴ Its surface area
= [Lateral surface area] + [Base area]
= [2(1 + b)h] + [lb]
= [2(1.50 + 1.25)0.65] m2 + [1.50 x 1.25] m2
= [2 x 2.75 x 0.65] m2 + [1.875] m2
= 3.575 m2+ 1.875 m2 = 5.45 m2
∴ Area of the sheet required for making the box = 5.45 m2
(ii) Cost of 1 m2 sheet = Rs. 20
Cost of 5.45 m2 sheet = Rs. (20 x 5.45)
= Rs. 109
Hence, cost of the required sheet = Rs. 109
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