This section is from the book "The Tinman's Manual And Builder's And Mechanic's Handbook", by Isaac Ridler Butt. Also available from Amazon: The Tinman's Manual And Builder's And Mechanic's Handbook.
Rule. - Set the first term on B to the second on a; and against the third upon B is the fourth upon a.
1. If 4 yards of cloth cost 38 cents, what will 30 yards cost at the same rate?
Set 4 on b to 38 on a; and against 30 on b is 285 cents on A.
2. Suppose I pay 31 dollars 50 cents for 3 cwt, of copper, at what rale is that per ton? 1 ton = 20 cwt.
Set 3 upon b to 31.5 upon a; and against 20 upon b is 210 upon a.