Question

Lea buys 20 picture frames. Some are 4 in. by 6 in. frames which cost $5.80 each, and the rest are 5 in. by 7 in. frames that cost $9.60 each. She spends a total of $80.80.
Which equation models this situation?

Let f represent the number of 4 in. by 6 in. frames she buys.

A.
9.6f + 5.8(20) = 80.8

B.
5.8f + 9.6(20 – f) = 80.8

C.
(5.8 + 9.6)(20 – f) = 80.8

D.
9.6f + 5.8(f + 20) = 80.8

Answer 1

To find the answer we have to slowly analyze the command.
 For surely on the one side we want to have total cash spent, so 80.8$
We know that there are 2 types of frames 5,80$ and 9.60$.
We know too, that f is the number of frames 5.80$ bought.
Simply, to find the cash spent on those frames we have to just mulitply 5.80$ times f, so we obtain $f*5.8$.
We can say that number of bigger frames is 20-f.
So to find cash spent on bigger frames we have to multiply 9.60$ times (20-f), so
$9.60*(20-f)$
Now we can just add cost of all frames together
$f*5.80+9.60(20-f)$
And we know that is equal to 80.8, so
$f*5.80+9.60(20-f)$=80.8

As we can see, the answer is b.