There are 20 rows of seats on a concert hall: 25 seats are in the 1st row, 28 seats on the 2nd row, 31 seats on the third row, and so on. How many seats are in the last row?

It is a sequence topic.

The general term of the sequence is 25+3(n-1) where n is the number of the term (here it is the row no.)

So the 20th term is the term with n=20. Substitute n=20 into the above general term, we will get 25+3(20-1) .

Please go on by yourself to work out the answer.

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".

the answer is simply just 6n add the two together as they have an n