For help! About OG11th Maths

xiaoy791

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The N.O. 123 question in OG 11th:

123. The price of lunch for 15 people was $207.00, including a 15 percent gratuity for service. What was the average price per person, EXCLUDING the gratuity?

A.$11.73

B.$12.00

C.$13.80

D.$14.00

E.$15.87

My answer is 207x(1-0.15)/15=11.73  (A)

But the standard answer goes to B.

cjwbhu

按每个人都收取了15%的gratuity，算出来就是12

xiaoy791

以下是引用cjwbhu在2008-9-7 11:23:00的发言：
按每个人都收取了15%的gratuity，算出来就是12

Each 15% is the same to All 15%, Please indicate how to calculate? Thanks

cjwbhu

设每人 average price 是x，则有1.15x*15=207，求得x=12

xiaoyuan2008

每人x，可得

15x*（1+15%）=207

x=12

xiaoy791

AND NO.115

Mary's income is 60 percent more than Tim's income,and Tim's income is 40 percent less than Juan's income. What percent of Juan's income is Mary's income？

A.124%

B.120%

C.96%

D.80%

E.64%

My solution process is: M=1.6T and T=0.6J,so M=1.6x0.6J,then J/M=1/(1.6x0.6)=104%

But the answer gives C 96%

Why? Confused!!!

cjwbhu

What percent of Juan's income is Mary's income？是m/j吧？

xiaoy791

Thanks a lot, I know what the problem is!