Mathematics for IGCSE & O level - Limits Of Accuracy (Section 2 - No. 14)

What is the minimum possible difference in length of two strings if one is measured at 20.0 cm and the other is 12.0 cm to the nearest mm?

7.9 cm

7.95 cm

8.0 cm

8.05 cm

Since the strings were measured to the nearest mm, this is equivalent to 1 d.p. This means the lower bounds are 19.95 - 12.05 = 7.9 cm