Question

A cistern $6$m long and $4$m wide contains water up to a depth of $1$m $25$cm. The total area of the wet surface is:

• A. 49$m^2$
• B. 50$m^2$
• C. 53.5$m^2$
• D. 55$m^2$

Answer 1

The correct option is A 49$m^2$

Consider it as a cuboid of length $=6m$, width $=4m$ & height $=1.25m$

What we have to calculate is ( total surface area of cuboid -surface area of top).

Since water will be wetting the surface in contact & these surfaces area the four walls & the bottom

surface area of walls $=a+b+c+d$

$6\times 1.25+6\times 1.25+4\times 1.25+4\times 125$

$=25m^2$

Surface area of bottom $=6\times 4=24m^2$

total area of water surface $=25+24=43m^2$.