Please help! Seven plates, 9.5lb, red and black, the red weigh 0.2 less. How much does each colour weigh?

Question

There are seven plates. 5 plates are red, 2 plates are black. In total, they weigh 9.5 pounds (lb). All red plates weigh the same, all black plates weigh the same. If the red plates are 0.2(lb) less than the black plates, how much does each red plate and each black plate weigh?

Answer 1

black plates weigh x lb

 

red plates weigh (x - 0.2) lb

 

5(x - 0.2) + 2x = 9.5

 

5x - 1 + 2x = 9.5

 

7x - 1 = 9.5

 

7x = 10.5

 

x = 1.5 lb

 

Black plates weigh 1.5 lb each

 

Red plates weigh 1.5 - 0.2 = 1.3 lb each