Question

15 workers can lay a road of length 4 km in 4 hours. Th en, _____ workers can lay a road of length 8 km in 8 hours. (3 marks)

Answer 1

Let the required number of workers be x.

Length	Hour	Workers
4 km	4 hrs	15
8 km	8 hrs	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)
Combine equation (1) and (2)
Product of the extremes = product of the means
4 x 8 x $x$ = 8 x 4 x 15
$x$= (8x4x15)/(4x8) x = 15 workers
(3 marks)