l另一小六题

痛过的人

Mr teo imported 78 more black caps than yellow caps. he sold 6/13 of the black caps and 3/4 of the yellow caps. he was left with 87 more black caps than yellow caps.
a:how many black caps did he import?
b:how many yellow caps did he sell?:L

4justice

if  he imported   x black caps and Y Yellow caps, then he sold  6X/13 black caps and 3Y/4 yellow caps., and he left  (X-6x/13) black caps and (Y-3Y/4) yellow caps.  

X- Y = 78 -----------------(1)
(X-6x/13) - (Y-3Y/4) = 87 -------(2)

X=  234;  Y= 156
a) he imported  234  black caps.
b)he sold  3/4 X 156 =  117  yellow caps.

痛过的人

黑色比黄色多 应该减78吧

doueyuan

回复 痛过的人 的帖子

13b-4r=78
7b-r=87
20b-5r=165
4b-r=33
3b=54
b=18
4b=72,r=72-33=39
a)18*13=
B)3*39=

g_qq

yellow:4units
black:4units+78
after sold:yellow,1unit;black,4*7/13unit+78*7/13=28/13unit+42,
difference is 15/13unit+42=87
so1unit=39
a)39*4+78=234
b)39*3=117

sunflower77

楼上解法很好。不过，a) 和b)问题搞反了，应该换下位。

shima

多贴一道同样类型的题，可用#5的解法。

Marina has 200 more books than Ehtel. Marina gives 60% of his books to Ethel. Then Ethel gives 25% of his books back to Marina. In the end Ethel has 200 more books than Marina. How many books does Marina have at first? (ans: 750)  

sunflower77

回复 shima 的帖子

楼上仔细查一下：题目是否有打错的地方。按你的条件，得不出你的answer。相信是你不小心什么地方敲错了。

shima

回复 shima 的帖子

我确认过了，题目没错，这是09年SCG SA1 Q18.

我的解法：
At first:
Marina :5U+200
Ethel: 5U

After Marina give 60% to Ethel:
M:2U+80
E:8U+120

After Ethel gives 25% back to Marina:
M: 4U+110
E: 6U+90
(4U+110) +200=6U+90
U=110

Marina at first : 5U+200=750

另一解法：
Marina :                 Ethel
200 + 100u    :         100u
80 + 40u        :         160u + 120
110 + 80u      :         120u + 90

120u + 90 = 80u + 110 + 200
40u = 220
u = 5.5

Marina at fist
200 + 100u
200 + 100x 5.5 = 750

你觉得题目中缺少什么条件呢？

sunflower77

回复 shima 的帖子

Sorry. I misunderstood one of the third sentence as  I neglect the word "then". You are absolutely right!