• # question_answer If two cubes of sides 9 cm each are joined end by end then the surface area of cuboid will A)  800 $c{{m}^{2}}$                B)  810 $c{{m}^{2}}$   C)  820 $c{{m}^{2}}$                D)  830 $c{{m}^{2}}$

(b): As we know, surface area $=6{{a}^{2}}$ Two cubes joined $\Rightarrow$Total surface area $=2\times 6{{a}^{2}}-$ surface area of two cubes at joints $\Rightarrow 12{{a}^{2}}-2\times {{a}^{2}}=10{{a}^{2}}=10\times {{9}^{2}}=810.$