We're useless at choosing between time-saving options

For a 100km trip, which saves more time?

a)Travelling at 50km/h instead of 40km/h.
b)Travelling at 130km/h instead of 80km/h.

a)Travelling at 50km/h instead of 30km/h.
b)Travelling at 130km/h instead of 60km/h.

"If you're like most of the participants in Svenson's study, you will have assumed that option (b) in both pairs is the most time saving. In fact, for the first pair, the time saved is equal (allowing for rounding off), and for the second pair, option (a) saves more time. From analysing participants' judgements, Svenson found that people seem to be mistakenly comparing the ratios of the two changes in speeds - applying what she calls the Ratio Rule."