There are 12 boxes of books to put on shelves . each box has 31 books. each shelf holds 18 books. kevin estimates he will need 20 shelves for all the books

21 shelves

Step-by-step explanation:

I'm going to guess that you want to know if Kevin is correct in his estimate.

How many books are there is total?

12 boxes * 31 books/box = 372 books in total

Each shelf will hold 18 books so

372 books * [1 shelf /18 books] = 20.6666 shelves.

To be safe unless he wants to stake some of the left over books, he will need 21 shelves. You have to round up for the left over books. 20 shelves is a good estimate, but you will need just one more that has 1/3 of a shelf left over. He can put a picture of his family there.

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".

answer: 1722

step-by-step explanation:

given: the mass of saturn=

the mass of mercury=

the number of times the mass of saturn is greater than the mass of mercury

hence, the mass of saturn is 1722 times greater than the mass of mercury.