Let the required number of workers be x
Length and workers are direct variable as more length need more workers.
The proportion is 4 : 8 : : 15 : x ……….(1)
Hours and workers are indirect variables as more working hours need less men.
∴ The proportion is 8 : 4 : : 15 : x ………..(2)
Combining (1) and (2)
Product of the extremes = product of the means
4 × 8 × x = 8 × 4 × 15
x = (8×4×15)/(4×8)
x = 15 workers
