Question

60% of the marbles in a container are red and the rest are black. After another 9 black

marbles are added, the ratio of red and black marbles becomes 4: 3. How many black marbles
are there now?

Answer 1

81

Explanation:

Red marbles = r

Black marbles = b

Red : Black

60 : 40

r : b

40r = 60b

r = (60/40)b

Red : Black

4 : 3

r : b + 9

3r = 4(b+9)

3r = 4b + 36

3((60/40)b) = 4b + 36

(9/2)b = 4b + 36

(9/2)b - 4b = 36

(1/2)b = 36

b = 72 This is the original amount of black marbles

They added 9 after this, so

72 + 9 = 81