
By: LeowML (offline) Friday, June 22 2012 @ 08:03 AM CDT (Read 1048 times)



LeowML 
At a school annual camp, the pupils were divided into two groups. At first, there were 600 pupils in group A and 30% were boys. There were 400 pupils in group B and 60% were boys. After some pupils were transferred from group B to group A, 40% of the pupils in group A and 60% of the pupils in group B were boys. How many pupils were transferred from group B to group A?

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Registered: 12/31/06 Posts: 11





By: echeewh (offline) Friday, June 22 2012 @ 07:19 PM CDT



echeewh 
Hey Leow,
this question is very much similar to the RGS Prelim 2011 Q16 that I posted earlier with the worked solution.
Anway heres the worked solution to this question of yours.

<Before>
Gp A: 600
Boys(B ) = 30% = (30/100) x 600 = 180
Girls(G) = 420
Gp B: 400
Boys(B ) = 60% = (60/100) x 400 = 240
Girls(G) = 160
<process>
some pupils were transferred from group B to group A
<After>
Gp A:
B : G
40 : 60
2 : 3
Gp B:
B : G
60 : 40
3 : 2
Applying <Unchanged Total> concept,
Number of Boys in A,B remain unchanged <Before> and <After> and,
Number of Girls in A,B remain unchanged <Before> and <After>
B: 2p + 3u > 180 + 240 = 420  (1)
G: 3p + 2u > 420 + 160 = 580  (2)
Eliminating (p):
(1)x3: 6p + 9u > 1260  (3)
(2)x2: 6p + 4u > 1160  (4)
(3)(4):
9u  4u > 1260  1160 = 100
5u > 100
1u > 20
Number of pupils in B (After) = 5u > 5 x 20 = 100
Number of pupils in B (Before) = 400
Therefore, number of pupils transferred from B = 400  100 = 300
=======================================
Trust this helps.
Do let me know again if this is different from your answerkey.
Cheers,
Edward.

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Registered: 04/21/11 Posts: 627





By: LeowML (offline) Sunday, June 24 2012 @ 10:38 PM CDT



LeowML 
The answer is correct. Thanks for your reply, Edward.

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Registered: 12/31/06 Posts: 11



