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 By: LeowML (offline)  Thursday, July 12 2012 @ 08:35 AM CDT (Read 991 times)
LeowML

Laura and Ahmad have some stamps. If Laura gives 80 stamps to Ahmad, he will have five times the number of stamps as she has. If Ahmad gives 120 stamps to Laura, she will have 1/3 as many stamps as Ahmad. how many stamps does Laura have at first?

Newbie

Registered: 12/31/06
Posts: 11

 By: echeewh (offline)  Thursday, July 12 2012 @ 08:12 PM CDT
echeewh

Hi Leow,

Following pls find my worked solution:

<After - 1st IF>

A |-------|-------|-------|-------|-------|
L |-------|

Apply <Work Backwards> to <Before> model

<Before>

*********************************-80
********************************<--
A |-------|-------|-------|-------|-----| --> (5p - 80)
L |-------|--| --> (1p + 80)
*********-->
*********80

<After - 2nd IF>

**<-------------3u---------------->
******************************-120
******************************<---
A |-------|-------|-------|-------|--| --> (5p - 200)
L |-------|--|---| --> (1p + 200)
***********--->
***********120
**<-----1u---->

From above models, we have ...

3u --> 5p - 200
1u --> 1p + 200

Rearranging above equations, we have ...

5p - 3u --> 200 --- (1)
1u - 1p --> 200 --- (2)

Eliminating (u):
(2)x3:
3u - 3p --> 600 --- (3)

Comparing (1),(3):
(1)+(3):
5p - 3p --> 200 + 600
2p --> 800
1p --> 400

Number of stamps L have at first = 1p + 80 --> 400 + 80 = 480

========================================

Trust this helps.

Do let me know again if this is different from your Answerkey or if there are any clarifications.

Cheers,
Edward

Active Member

Registered: 04/21/11
Posts: 627

 By: LeowML (offline)  Tuesday, July 17 2012 @ 06:43 PM CDT
LeowML

Dear Edward,