maths

👨🏻‍🏫 學術台數學

[匿名]

2012-05-14 8:46 am

Mary sold two bags for $240 each.She gained 20% on one and lost 20% on the other.After the two transaction.Mary

A:lost $20

B:gained $10

C:gained $60

D.had no gain and loss

which in correct and why?

更新1:

Dion: 點解係divide??

更新2:

咩係名數??

回答 (3)

用戶50068

2012-05-20 1:30 am

(selling price- cost price)/cost pricex100%=20%

(240-c)/c=1/5
240-c=c/5
240=c/5+c
240x5=5(c/5+c)
1200=c+5c
1200=6c
c=200
(E個系EARN的)

(cost price- selling price)/cost pricex100%=20%
(c-240)/c=1/5
c-240=c/5
-240=c/5-c
5(-240)=5(c/5-c)
-1200=c-5c
-1200=-4c
c=300
(E個系LOST)

300+200=500(totally cost)
240*2=480(selling price)
500-480=20
so, he lost $20

the correct answer isA

參考: me

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Laura

2012-05-14 8:41 pm

要還原番就要divide,名數除名數等於不名數

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Dion

2012-05-14 9:13 am

A: lost $20

1st bag (gained 20%):
sold for $240
cost = 240 / (1+20%) = $200
gained $40

2nd bag (lost 20%):
sold for $240
cost = 240 / (1-20%) = $300
lost $60

40-60= -20
Mary lost $20

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