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help needeeeeed!!! ( sets )

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help needeeeeed!!! ( sets )

by marmar29 » Tue Feb 15, 2011 12:15 am
in a school ,Ss must take at least one of these subjects : math, chem,or physics
in a group of 50 Ss, 7 take ol the 3 subjects , 9 take ph & ch only , 8 tk math & ph pnly , 5 tk math n ch only .of these 50 ss, x take math only , x take physics only ,x+3 take ch only . draw a venn diagram , find x & find the number taking math ????
pls i need it in brief way n the rule tht u used

PS ..is ths for extended IG or A -LEVEL ...THANNKS
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by vaflaly » Tue Feb 15, 2011 1:29 am
total= only(math) + only(phys)+ only(chem)+ both(math&phys)+both(chem&phys)+both(math&chem)+ all3

only(math)= x
only(phys) = x
only(chem)= x+3

total(math&phys)= only(math) + only(phys) - both(math&phys)
both(math&phys)= 2x-8
In the same way, both(math&chem)=2x-2
both(chem&phys)=2x-6

remember all3 is number of students learning the 3 subject s

50= x + x + x+3 + 2x-8 + 2x-2 + 2x-6 + 7

x=7


Drawing a wenn diagram is good to have a clear view
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by srcc25anu » Tue Feb 15, 2011 1:52 pm
total (50) = only M(x) + only Phy (x) + only Chem (x+3) +M &Phy only (8) + M&Chem only (5) + phy and Chem only (9) + all three (7)
x=6
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by marmar29 » Tue Feb 15, 2011 8:36 pm
thanks for yr active replay but if we sub. 7 in the equation the final result wont be 50 !!
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by marmar29 » Tue Feb 15, 2011 8:38 pm
hi srrc, thanks alooot for yr active response
its very weasy n straight forward ...it really helps !
have a good day
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