How many photos can 11Gb hold?

That depends on what camera you are using (the size of the sensor) and the quality chosen to save the images, as well as the compression algorithm used. Some cameras will not fit a single image into 11Mb others (like my Panasonic at lowest quality) will fit 40 or so (more if I take pictures of the sky or areas that have little detail, because the jpeg compression algorithm can compress bland subjects more easily than complex ones).