In an enrichment class,1/3 are boys and the restare girls.After 3 girls and 3 boys leave the class,there are now 2/5 as many boys as girls.How many pupils are there in the class in the end?
问题描述：
In an enrichment class,1/3 are boys and the restare girls.After 3 girls and 3 boys leave the class,there are now 2/5 as many boys as girls.How many pupils are there in the class in the end?
答
30
1/3a-3=2/5(2/3a-3)
a=36
a-6=30
答
我们假设男生为x，女生为y,开始时候的学生总数为z.
则有x+y=z, x-3=2/5(y-3) 由于x=1/3z,y=2/3z
可求出z=27,x=9,y=18.
最后人数=（9-3）+（18-3）=21
答
在一个班级里,三分之一是男生,剩下的都是女生.3个男生和3个女生离开班级以后,现在男生人数是女生的五分之二.最后班里还有多少小学生?
21人.
设原来男生有x人,则原来女生有2x人.
x-3/2x-3=2/5
解得x=9
则现在班里有9×3-6=21（人）.