Aschool has 18 classes with 35 students in each class. in order to reduce class size to 30, how many new classes must be formed?

18*35 - number of the students at school.

x- is a number of classes if it is going to be 30 students per class, then

30x - number of the students at school.

So,

18*35 = 30x

x=(18*35)/30 = 21 classes should be if it is going to be 30 students per class.

21 - 18 = 3 new classes must be formed.

he used the algebra tiles correctly.

step-by-step explanation:

given : 3x(2x-1)

solution :

since he used algebra tiles .

armando's solution is the same in the solution shown in figure

as he distributed 2x into x and x and wrote them vertically

and also write   -1 vertically

and 3x into x and x and x and wrote it horizontally

performing the multiplication in the algebra tiles we get

and solving the given expression :

3x(2x-1)

since solving the expression using tiles   and solving the expression algebraically we get the same answer

thus   we can choose the first statement as the answer to this problem which is "he used the algebra tiles correctly".