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Sagot :
Answer:
81
Step-by-step 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
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