'1000 Gigabytes is equal to 1 Terabyte; 1000 Terabytes is equal to 1 Petabyte; How many Gigabytes are in a Petabyte?'
would be [a. 1,000,000 Gigabytes]
or
'1024 Gibibytes is equal to 1 Tebibyte; 1024 Tebibytes is equal to 1 Pebibyte; How many Gibibytes are in a Pebibyte?'
would be [a. 1,048,576 Gibibytes]
If your going to use binary numbers, you should use binary prefixes. And by all means keep the answer in binary at the very least. The two can not be mixed with out conversion, which confuses the hell out of me thinking about converting from one to the other. I have to lay it all out in Excel to keep them straight.
I don't really care about the naming issue, but 1024 * 1024 isn't 1,000,000. Sure, that's the closest answer, which is probably why people vote for it, but it's still completely and utterly wrong.
Frankly I dislike this naming scheme. Apart from being used to 'kilobyte' (which is what 1024 bytes were called for most of my life), Kibibyte just sounds silly, kawaii bytes, chibi-bytes. Perhaps I'm an old fart, but I just don't think the IEC made a good choice when proposing this.