Question

A classroom is 7 m long, 6 m broad and 3.5 m high. Doors and windows occupy an area of 17 m². What is the cost of white-washing the walls at the rate of Rs 1.50 per m².

Answer 1

\[\text { Length of the classroom = 7m } \]

\[\text { Breadth of the classroom = 6  }m\]

\[\text { Height of the classroom = 3 . 5 m }\]

\[\text { Total surface area of the classroom to be whitewashed = areas of the 4 walls }\]

\[ = 2 \times \text { (breadth } \times\text {  height + length } \times \text { height })\]

\[ = 2 \times (6 \times 3 . 5 + 7 \times 3 . 5)\]

\[ = 2 \times (21 + 24 . 5)\]

\[ = 91 m^2 \]

\[\text { Also, the doors and windows occupy 17 } m^2 . \]

\[\text { So, the remaining area to be whitewashed  }= 91 - 17 = 74 m^2 \]

\[\text { Given that the cost of whitewashing 1 } m^2\text {  of wall = Rs  }1 . 50\]

\[ \therefore \text { Total cost of whitewashing 74 } m^2 \text { of area } = 74 \times 1 . 50 = Rs 111\]