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Answer:
a) 35, b) 25, c) 60
Step-by-step explanation:
The number of girls is 10 more than the number of boys, so it's a good thing to choose a variable to represent the number of boys.
Number of boys: b
Number of girls: b + 10
Ratio of girls:boys is 7:5, so
"Cross multiply" to get
There are 25 boys. There are 10 more girls, so the number of girls is 35, and the total number of students is 60.
That's a packed classroom!
Assuming that each marble can be picked with equal probability, we notice that there is a total of
marbles, of which 2 are red.
So, the probability of picking a red marble is
In fact, as in any other case of (finite) equidistribution, we used the formula