I assume you mean PERCENTAGES right? Well if you do then some of the most common percentages are 50%, 75%, 25%, 80%, and many more some random ones I just thought of nw are 30%, 41% etc. I hope that's what you meant and I hope I helped?
Answer:
he is correct he might have seen it's 3 times more than 18-29 which is 10% so he just multiplied 45 with 3