Step-by-step explanation:
there are 50 students and 5 prizes (1 + 1 + 3).
so, already in natural language we would say "there is 1 prize for every 10 students".
formally, remember the rule of probability : desired outcomes over total possible outcomes.
this is here
5/50 = 1/10 = 0.1
your can see it also this way :
if there was only 1 prize, each student would have a chance of 1/50 of winning.
now there are 5 prizes, which gives everybody 5 times the chance of winning. which is then 5×1/50 = 5/50 = 0.1
