Could someone please help me figure out what is going on here?

I have the following in a spreadsheet:

Cell BQ16 = 536 - a raw number
Cell BQ17 = 509 - correctly derived from the formula:
(=INDEX(HourlyData!$A$2:$Z$355,MATCH('Efficiency July-Dec
07'!BQ$3,ManpowerData!$A$2:$A$355,0),2)

In Cell BQ18 I have the formula =BQ17/BQ16 formatted as a percent - should
be 95% but it calculates 0%.

When I place this formula in BQ18 =BQ16/BQ17 I get the #DIV/0! error. Why?
I see 509 in BQ17, not zero. Why does excel think it is a zero?

Am I not able to do a calculation using a number in a cell generated by an
index match function? Or is this something else?

Thanks,
Diane