Question 1084916
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 radius of the pool = 3.5 m; the overall radius including the border = 5.5m
 Find the area of the concrete border
overall area - pool area = border area
A = {{{pi*5.5^2}}} - {{{pi*3.5^2}}}
A = 56.55 sq m
: 
 The concrete needs to be 50 millimetres deep.
Find the volume of the concrete, change 50 mm to .05 m
56.55 * 05 = 2.8275 cu/meters
:
 You are using premixed bagged concrete.
 1 cubic metre (m³) requires 106 x 20 kg bags.
find the no. of bags
106 * 2.8275 = 300 
 How many 20 kg bags of premixed concrete do you need?
300 bags 
 Round your answer to the nearest whole number. 

:
Corrections made 1-18-2018.