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 By: LeowML (offline)  Friday, June 22 2012 @ 08:03 AM CDT (Read 1063 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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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.

Active Member

Registered: 04/21/11
Posts: 627

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