Cost of Boring.
The cost of boring when executed by contract has already been treated of at page 80. The following formula will furnish the same results as the rule there given, but with the least possible labour of calculation;
x = 0·5d(·187 + ·0187d);
x being the sum sought, in pounds, and d the depth of the boring in yards.
Example. Let it be required to know the cost of a bore-hole 250 yards deep.
Here 125{·187 + (·0187 × 250)} = £607·75.