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 By: Strawberry (offline)  Thursday, August 16 2012 @ 09:51 AM CDT (Read 914 times)
Strawberry

There are some black and white marbles in a bag. If 20 black marbles are removed from the bag, the total number of marbles left will be 7 times the number of black marbles left.
If 50 white marbles are removed from the bag, the total number of marbles left will be 5 times the number of black marbles left. How many marbles are there in the bag?

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Registered: 01/31/09
Posts: 83

 By: awyw1201 (offline)  Friday, August 17 2012 @ 10:11 AM CDT
awyw1201

Use units and parts

If 20 black marbles are removed, ratio of B:W--->1u: 6u

If 50 white marbles are removed, ratio of B:W--->1p:4p

No. of black marbles--> 1u + 20 = 1p ----(1)

No. of white marbles--->6u = 4p + 50 ---(2)

(1) x 4, we have---------> 4u + 80 = 4p ---(3)

Substitute (3) into (2), we have---> 6u = 4u + 80 + 50

Thus, 2u = 130

1u = 65

65 x 7 + 20 = 475

Ans: 475

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Registered: 07/08/11
Posts: 87

 By: Strawberry (offline)  Friday, August 17 2012 @ 11:58 AM CDT
Strawberry

thanks

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Registered: 01/31/09
Posts: 83

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