She saved 10 shots out of 18 total, so that means 18-10 = 8 shots went in.
That forms the ratio 8:10 where we list the amount of shots that went in, followed by a colon, then the amount of shots that were saved. The order is important. From here, we divide both parts of the ratio by 2. The ratio 8:10 fully reduces to 4:5
Effectively, this means that for every 4 shots that went in, there were 5 shots that were blocked.