A swimming pool is 20m long and 8m wide. It is 3.5m deep. A concrete slab 30cm thick is to be poured around the pool. Calculate the volume of concrete needed.

Here are the calculations for the swimming pool problem. I'll assume the pool dimensions are Length = 20m and Width = 8m, based on the phrasing "length 20 eight m", and a depth of 3.5m as stated in the text. The diagram's '30m' will be disregarded as it conflicts with the text's ambiguous length description.

Given parameters:

• Pool Length ($L$) = 20 m
• Pool Width ($W$) = 8 m
• Pool Depth ($D$) = 3.5 m
• Concrete thickness ($t$) = 30 cm = 0.3 m
• Bulk coefficient for soil