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 Forum Index >  Test Paper Related >  Primary 6 Matters
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By: amandal (offline)  Thursday, August 08 2013 @ 03:28 AM CDT (Read 505 times)  
amandal

need some help on the following Qns

Catherine has a box containing some black and white counters. When she add in 15 white counters, 65% of the counters in the box are black. If she adds in another 40 black counters, 75% of the counters in the box are black. How many white counters are there in the box at first ?

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By: eqkt (offline)  Thursday, August 08 2013 @ 07:23 AM CDT  
eqkt

Hi Amandal,
Skip the first information of the question.

Black : White
13u : 7u
+40
___________
3u : 1u (1u x 7)
(3u x 7)

There should be the same number of white counters in the top white and the bottom white, thus we x 7 for the bottom white to make it the same as the top white.

21u-13u=8u
8u----> 40
1u----> 40/8 =5
5 x 7=35
35-15=20 (came back to the first information of the question)


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