Question

2. The length, breadth and height of a room are 5m, 4m and 3
respectively. Find the cost of white washing the walls of the room and
the ceiling at the rate of Rs. 7.50 per m ​

Answer 1

GIVEN :-

• Length (l) = 5m
• Breadth (b) = 4m
• Height (h) = 3m
• Cost of white washing is 7.5Rs/m².

TO FIND :-

• Cost of white washing the walls and ceiling.

TO KNOW :-

★ Lateral Surface Area of Cuboid = 2(lh+bh)

★ Area of base of Cuboid = lb

SOLUTION :-

We have to find the area of walls and the ceiling.

Area for white washing = L.S.A + base area

= 2(lh+bh) + lb

Putting values we get...

→ 2[ (5)(3) + (4)(3) ] + (5)(4)

→ 2[ 15 + 12 ] + 20

→ 2 [ 27 ] + 20

→ 54 + 20

→ 74m²

Hence , area of 74m² room is to be white washed at the rate of 7.5Rs/m².

_____________

We know ,

Cost of white washing is 7.5Rs per metre.

1m² → 7.5Rs

For 74m , Cost of white washing will be 7.5×74 Rs.

74m² → 7.5 × 74

ㅤㅤㅤ→ 555Rs

Hence , cost of white washing is 555Rs.

MORE TO KNOW :-

★ Area of cube = 6×edge²

★ Area of cylinder = 2πr(r+h)

★ Area of cone = πr(r+l)

★ Area of hemisphere = 3πr²

★ Area of sphere = 4πr²

Answer 2

Given :-

Length = 5m

Breadth = 4m

Height = 3m

To find :-

Cost of white washing of room and ceiling.

Using Formula :-

LSA of rectangle + Base Area

= 2h (l + b) + lb

Solution :-

Length = 5m

Breadth = 4m

Height = 3m

Area of white washing = 2h (l + b) + lb

= 2 × 3m (5m + 4m) + 5m × 4m

= 6m (9m) + 20m²

= 54m² + 20m²

= 74m²

Therefore,

Area of white washing = 74m².

Cost of white washing 1m² = Rs.7.50

Cost of white washing 74m² = 7.5 × 74 = 555

Therefore,

Cost of white washing = Rs.555