At first, the ratio of dave's savings to sam's savings was 5: 4. after each of them donated $40 to charity, the ratio of dave's savings to sam's savings became 13: 10. what was dave's savings at first?

$300  

Step-by-step explanation:

Let D = Dave's savings and S = Sam's savings.

(1)                     D/S = 5/4

(2) (D – 40)/(S-40) = 13/10                  Multiply (1) by 4S

(3)                     4D = 5S                      Multiply (2) by 10(S-40)

            10(D - 40) = 13(S - 40)            Remove parentheses

(4)       10D – 400 = 13S - 520            Solve (3) for S

                         S = (4/5)D                  Substitute into (4)

         10D – 400 = 13(4/5)D - 520     Multiply each side by 5

     50D – 2000 = 52D – 2600         Subtract 50D from each side

               -2000 = 2D – 2600            Add 2600 to each side

                  600 = 2D                          Divide each side by 2

                      D = $300

Dave's savings at first were $300.

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: idk

step-by-step explanation: