Question

Shereda bought several dozen roses and several dozen carnations. The roses cost $15 per dozen, and the carnations cost $8 per dozen. Shereda bought a total of 17 dozen flowers and paid a total of $192. How many roses did she buy?

Answer 1

Write down what you know, and assign letters to your variables:

r = number of roses (in dozens)
c = number of carnations (in dozens)

Total cost = T = 192
Total number of flowers (in dozens) = F = 17

Then:
15r + 8c = 192
15r = 192 - 8c
15r/8 = 24 - c
c = 24 - 15r/8

r + c = 17
c = 17 - r

Therefore:
17 - r = 24 - 15r/8
-r + 15r/8 = 24 - 17
7r/8 = 7
r = 8 dozen roses

Answer 2

why is it 7r/8 at the end?

Answer 3

please help

Answer 4

Because -r + 15r/8 = 15r/8 - 8r/8 = 7r/8