妞在学校做了一道ratio题，答案是81,可我得到的答案是63，到底哪个对，为啥呀
题目如下：
The ratio A to B is3:4,If 18 people join B,the ratio is now 1:2, How many people are there in total?
评论
Original A & B with total 7 units (i.e. 3+4)
After 18 people join B ... A & B total with 9 unit (1:2 = 3:6 ...3+6 = 9)
9 units - 7 units = 18 people ... so 1 unit = 9 people (18 people/(9-7))
Total (Original) = 9 people x 7units = 63 people
Total (After 18 people joined) = 9 people x 9units = 81 people.
CHECK 81-63 people = 18 people (i.e. correct)
评论
忽略了新加入的18人啦
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是的，应该是81.
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63是原来AB的总数，81 算上了后来的18个人
A/B= 3/4 ； A/（b+18)= 1/2 => A =27 ,B=36
评论
参考我给你的另外一道题的图解法来解释。
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