An open box is made of wood 3 cm thick. Its external length, breadth and height are 1.48 m, 1.16 m and 8.3 dm. Find the cost of painting the inner surface of Rs 50 per sq. metre.
Length of open wood box (L) = 1. 48 m = 148 cm
Breadth (B) = 1.16 m=116 cm
and height (H) = 8.3 dm=83 cm
Thickness of wood = 3 cm
∴ Inner length (l)=148−2×3=148−6=142 cm
Breadth (b)=116−2×3=116−6=110 cm
and~height~(h) = 83−3=80 cm
∴ Surface area of inner of box=2h(l+b)+l×b
=2×80[142+110]+142×110 cm2
=160[252]+142×110 cm2
=160×252+142×110 cm2
=40320+15620 cm2
=55940 cm2=55940100×100 m2=5.594 m2
Rate of painting = Rs 50 per m2
∴ Total cost = Rs 50×5.594= Rs 279.70