Hello all. Long time listener, first time caller.
Why do some girls on AW have such a high marginal rate for 90 minutes as opposed to 60. For example, 1hr will be £90 and 2hrs £180 but 1.5hrs won't be £90x1.5=£135 but £150 meaning that extra 30 minutes is £120/hr! Another example is £150 for 1 hour but £250 for 1.5 hours instead of £225. Are they just bad at maths or are 90 minute bookings really such a hassle? I thought things were supposed to be cheaper in bulk?
I would say its to make the longer booking seem more attractive to the punter, so ultimately she gets more money out of you. In the example you state, you quite rightly point out that £100 for a half hour is a lot of money compared to the hourly rate, but then it makes you think £50 for the last half hour isn't so bad so you may as well go for 2 hours.
In a lot of cases, the WGs 2 hour rate is less than double for her hourly rate (say 2 hours for £250 if an hour is £150). In such a case, its definitely in her interests to make the 90 minute rate close to the 2 hour rate as it makes the 2 hour booking a better proposition for both of you, if she offers it at all.
Don't jump to the assumption that its because WGs are bad at maths- the vast majority are far from innumerate as far as the pound sign is concerned...