A small terrace comprises of 10 steps each of which is 15m long and made of solid concrete. Each step has a rise of 0.25 m and a tread of 0.5m. The total volume of concrete required is -

225 m³

Dimensions in 1st step = 15×0.25×0.5 m

Volume of first step = 1.875 cubic m

Dimensions of second step= 15×0.5×05m

Volume of 2nd step = 3.75 cubic m

Dimensions of 3rd step = 15×0.75×0.5 m

Volume of 3rd step = 5.625 cubic m

Now, we have 

a= 1.875

d= 1.875 and n=15

Sum of 15 terms can be calculated as follows:

S₁₅=\(\frac{15}{2}\)[2×1.875+14×1.875 ] = 225

Volume of concrete = 225 cubic m