Question

The cost of painting the internal surface of the tunnel (excluding the floor) at the rate of Rs. $5$ per $m^2$

• A. Rs. $2040$
• B. Rs. $2000$
• C. Rs. $2400$
• D. Rs. $2004$

Answer 1

Answer: (A)

Rs. $2040$

$AM=BN$ $=\frac{7-5}{2}$
$=\frac{2}{2}$
$=1m$
In $△ADM$
$A{D}^2=A{L}^2+D{L}^2$
$=>A{D}^2=1^2+{2.4}^2$
$=>A{D}^2=1+5.76$
$=>A{D}^2=\sqrt{6.76}$
$=>AD=2.6m$
Perimeter of the cross section of the tunnel $=(5+2.6+2.6+7)$
$=17.2m$
Length $=40m$
$\therefore$ internal area of the tunnel (except floor)
$=17.2\times 40-40\times 7$
$=688-280$
$=408m^2$
Rate of painting $=5$ per $m^2$
Therefore, total cost of painting the tunnel $=408\times 5$
$=$Rs. $2040$