The reason you're not getting the correct result is that multiple Find requests function as a logical OR. So you're finding anyone > 50 OR < 70 ... which is basically everyone. You need to put "50...70" instead in the field. This defines a range of desired values.
As an aside, it might be easier to do this all for the user in the scripting, if the range is always 50 - 70. You can write a script like this:
Enter Find Mode [ ]
Set Field [ yourField ; "50...70" ]
Set Error Capture [ On ]
Set Error Capture [ Off ]
If [ Get ( FoundCount ) < 1 ]
Show All Records
Show Custom Dialog [ "Error" ; "No records found" ]
If you really want to get fancy, you can put two global fields with low and high values and let the user choose. If you do that, some additional error trapping would be needed for a good user experience (make sure both values are populated, make sure the low value is lower than the high value, etc.).
Thanks Mike - it was the AND piece that stumped me.
On a similar theme, if I have a date field for the date of birth, how do I find all those people with birthdays in november ? I've tried /11/ etc but don't get an answer. Thanks
Just put "11" (without the quotes) in the field. FileMaker will change it to 11/*/2015 (or whatever the current year is).