A quality report on a garment unit says that 18 pieces out of every 1,000 stitched are rejected. What per cent of the pieces stitched are rejected?

A per cent is a count out of 100, so scale the figure down by 10: 18 out of 1,000 is 1.8 out of 100, that is 1.8%. In fraction form 18/1000 = 0.018 = 1.8%. 18% reads a figure quoted per thousand as though it were quoted per hundred - the commonest slip with these reports. 0.18% divides by 10,000, and 180% multiplies by 10 instead of dividing.