an open box is made of wood 3 cm thick its..., Area & Volume, General Mathematics

Question:An open box is made of wood `3` cm thick. Its external dimensions are `1.46 m``1.16 m` and `8.3 dm.` The cost of painting the inner surface of the box at `50` paise per `100` sq. cm is :

A `Rs. 277` 
B `Rs. 138.50` 
C `Rs.415.50` 
D `Rs. 554`

/113

+ AnswerA

+ ExplanationInternal length 

`= (146 - 6) cm = 140 cm,`

Internal breadth

`= (116 - 6) cm`

`= 110 cm.`

Internal depth

`= (83 - 3) cm`

`= 80 cm.`

:. Area of inner surface

`= [2 (1 + b) xx h] + 1b`

`= [2 (140 + 110) xx 80 + 140 xx 110] sq. cm`

`= 55400 sq. cm.`

Cost of painting `= Rs. (1/2 xx 1/100 xx 55400)`

`= Rs. 277`

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