Question

I’m stuck, please give the explanation for the first question.

Answer 1

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Define x:
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Let x be the number of students in the second class:
⇒second class = x

There are 3 more students in the first class than in the second class:
⇒first class = x + 3

There are 2 more students in the third class than in the second class:
⇒third class = x + 2

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Expression for each class:
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First class = x + 3
Second class = x
Third class = x + 2

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Expression for total number of students:
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Total = x + 3 + x + x + 2
Total =  3x + 5

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Find x:
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There are 80 students in total, so
3x + 5 = 80
3x = 75
x = 25

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Find the number of students in each class:
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First class = x + 3 = 25 + 3 = 28
Second class = x = 25
Third class = x + 2 = 25 + 2 = 27

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Answer: There are 25 students in the second class.
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Answer 2

you should write equation for this
if we put x as the number of students in the second class then the equation will be :
$(3 + x) + x(2 + x) = 80 \\ 3 + x + x + 2 + x = 80 \\ 5 + 3x = 80$
now you can find the value of x:
$5 + 3 x = 80 \\ 3x = 80 - 5 \\ 3x = 75 \\ x = \frac{75}{3} = 25$
the number of students in the second class is 25


you can find the others, too

first class: 25+ 3=28

third class: 25+ 2=27


good luck