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So there are five candy bars.
Herself and two sisters equals 3 people in total.
This is a graph of 5 candy bars, each line being 1/2.
━ ━
━ ━
━ ━
━ ━
━ ━
If she ate half of one... the graph would become this.
━ ━
━ ━
━ ━
━ ━
━
Now there are 9 halves. You need to split the 9 halves for 3 people. 9 divided by 3 is 3.
Each person gets 3 halves, or 1 and 1 half.
Mai: ━ ━ ━
Sister 1: ━ ━ ━
Sister 2: ━ ━ ━
Altogether that is 9 halves, AKA the number of halves Mai had after she ate 1/2.
The amount Mai ate in the first place: ━
9 halves plus 1 half, equals 10 halves. Each whole has 2 halves. 10 divided by 2 is 5, AKA the number of candy bars she had in the first place.
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Let's firstly convert the mixed fraction to "improper" and then proceed,

If you apply the or both
Only 1 of the students would need to know the "or both", therefore maximizing the remaining amount of students you can put in.
Gerald, let's call him, knows French AND German, so there's only one less student that knows french and german. Gerald is 1 student.
MAXIMUM:
There are now 14 monolinguistic French speakers and 16 monolinguistic German's, 30 students + Gerald=31.
Minimum:
As a bonus, the minimum is 15 students knowing french AND German and only 2 monolinguistic German speakers, so 17.
Answer:
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Step-by-step explanation: