Three cubes each of volume 343 cm3 are placed side by side. What will be the surface area of the solid so formed (in cm2)?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 686
Three equal cubes placed side by side form a cuboid three cubes long; its surface area is \(2(lb+bh+hl)\).
Side of each cube \(=\sqrt[3]{343}=7\) cm
Cuboid: \(l=21\) cm, \(b=7\) cm, \(h=7\) cm
Surface area \(=2(21\times7+7\times7+7\times21)=2(147+49+147)\)
\(=2\times343=\) 686 cm2
Shortcut:
Three cubes have \(3\times6=18\) faces; each of the 2 joins hides 2 faces, so \(18-4=14\) faces stay outside
Each face is \(7\times7=49\) cm2, so the area \(=14\times49=686\) cm2