The ratio of the number of children to the number of adults at a partywas 2:5. After 35 children and 35 adults joined the party, the ratio of the
number of children to the adults became 3:4. How many children were there at first?
我会设X列方程做，当然也可以猜着做，猜到5就做出来了。但这都不适合小五学生来理解。
请问有没有适合小五学生的解法？
谢谢
Constant difference
2:5 ( 5-2 =3) X1 ————->2:5
3:4 (4-3 =1) X3 ————-> 9:12
9u-2u = 7u = 35
1u= 5
2u = 10
there were 10 children at first
楼上正解，此类题，无非就是总数不变，差值不变。最难的就是什么都变的，就用交叉相乘。其实和解方程的概念是一样的，只是更加适合小学生去理解。
2/5 ==> 3/4; ( the ratio changed from 2/5 to 3/4 after additional 35 each children & adult added )8/20 ==> 15 / 20;8*u + 35 = 15 * ( u + 35/20 ); ( 8u is the original number of children )u = 1.25 ;8u = 10
同“fangchaoxx88”说的，基本意思是一样的，其它guess、list 之类的方法也可以玩玩，只要孩子能有兴趣接受就成。
1 unit — > 35/7 = 5
Children —> 5×2 =10
8u + 35 = 15*(u+35/20)
8u = 10
容易理解，赞一个！
感谢分享！刀如水的图一出，题目就解了大半，怎么样才能画出这样的图，用什么思路，我害的琢磨琢磨。