Question

A tank is  25m long,  12m wide and  6m deep. The cost of plastering its walls and bottom at 75 paise per sq m is

Answer 1

surface area of tank =2(lb+bh+hl)
l=25m,b=12,h=6
area of surface=2(25*12+12*6+6*25)
=2(300+72+150)=2*522=1044sq.m
cost=0.75*1044=783 rupees
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Answer 2

Cost of plastering walls and bottom at 75 paise/sq m is Rs.558.

Solution:

The length of the tank is 25m, the breadth is 12m, and the depth or the height of the tank is given as 6m.

The area of the tank is 25m and 6m on two faces of the tank i.e. a total of 2 area that consist of an area of $(25 \times 6)\ m^{2}$  . Therefore, the total area of the A sides are,

$2(25 \times 6)=2(150)=300\ m^{2}$

The area of the tank is 12m and 6m on two faces of the tank i.e. a total of 2 area that consist of an area of $(12 \times 6)\ m^{2}$  . Therefore, the total area of the B sides are,

$2(12 \times 6)=2(72)=144\ m^{2}$

Now as the C side is the bottom and we have to plaster the bottom only therefore, the area of the bottom part of C is $25 \times 12=300\ m^{2}$  Therefore, to calculate the price of plastering the total of all the area,

$(A+B+C)=\left(300\ m^{2}+144\ m^{2}+300\ m^{2}\right)=744\ m^{2}$

Now to find out the price required which is 75 paise/sqm.  

We multiply the price with the total area which has to be plastered.

i.e. $\bold{Area \times Price/sq\ m = 744\ m^{2} \times R s .0 .75=R s .558}$