AVERAGEIF: can't get around #DIV/0! error

Hi.

Forum noob here. Please be gentle.

I'm trying to get the arithmetic mean of a selection of numbers from a list of 100 values.

It's a survey of free speeds (motor traffic) and the complete list of numbers comprises 100 speed readings in kilometres per hour.

The speed limit on the road in question is 50 km/h, so I am trying to obtain (using AVERAGEIF) the mean speed of 'speeders'.

In other words, I want to calculate the average of all the readings greater than 50.

The data are in cells B24:B123, worksheet "Readings".

The reference value (in this instance 50 km/h) is in the user defined variable "speedlimit".

This is the formula I am using, and which gives the #DIV/0! error: =AVERAGEIF(Readings!B24:B123,">speedlimit")

I've tried various tweaks, but I always get the same error.

What am I doing wrong, and how can I fix it?

Thanks in advance.




EDIT: Incidentally, if I use =AVERAGEIF(Readings!B24:B123,">50") it works fine. However, I need to be able to have different values for the variable "speedlimit".