Question

You are laying a concrete border around a circular pond.

The pond is 7 metres in diameter and is surrounded by a path 2 metres wide.

The concrete needs to be 50 millimetres deep.



You are using premixed bagged concrete.

1 cubic metre (m┬│) requires 106 x 20 kg bags.

How many 20 kg bags of premixed concrete do you need?

Round your answer to the nearest whole number.

Answer 1

Answer: 300 bags of 20 kg  of prmixed are required.

Step-by-step explanation:

The diameter of pond, d= 7 m (given)

The radius of inner border of pond, r= d/2= 7/2 m

The radius of outer circular border, R= r+2= 7/2+2= 11/2m

Area of concrete border around the circular pond= area of outer circle- area of inner circle

So,

pi*R^2-pi*r^2= pi*(R^2-r^2)

=> 22/7*((11/2)^2-(7/2)^2)

=> 22/7*(121/4-49/4)

=> 22/7*72/4

=> 56.57 m^2

volume of concrete needed= area*height= 56.57*0.05= 2.8285 cubic meter

Since 1 cube meter requires 106 x 20 kg bags,

2.8285 cubic meters require bags= 2.8285x106x20 kg

20 kg bags of premixed concrete required= 2.8285x106x20/20

=> 2.8285x106

=> 299.821 or 300 approximately