请大侠帮我看看这几道题，不是很难

mataoturku

请大侠帮我看看这几道题，不是很难

Solution Y is 30 percent liquid X and 70
percent water. If 2 kilograms of water
evaporate from 8 kilograms of solution
Y and 2 kilograms of solution Y are
added to the remaining 6 kilograms of
liquid, what percent of this new solution
is liquid X?

After paying a 10 percent tax on all
income over $3,000, a person had a net
income of $12,000. What was the income
before taxes?

Working alone, R can complete a certain
kind of job in 9 hours. R and S, working
together at their respective rates, can
complete one of these jobs in 6 hours. In
how many hours can S, working alone,
complete one of these jobs?

谢谢

Solution Y is 30 percent liquid X and 70
percent water. If 2 kilograms of water
evaporate from 8 kilograms of solution
Y and 2 kilograms of solution Y are
added to the remaining 6 kilograms of
liquid, what percent of this new solution
is liquid X?

After paying a 10 percent tax on all
income over $3,000, a person had a net
income of $12,000. What was the income
before taxes?

Working alone, R can complete a certain
kind of job in 9 hours. R and S, working
together at their respective rates, can
complete one of these jobs in 6 hours. In
how many hours can S, working alone,
complete one of these jobs?

谢谢

royalex

（1），比例等于x/y，
x=30%*8+30%*2（第一次的含量+第二次加入的含量）
y=8-2+2,（第一次的总重量-蒸发的水量+加入的重量）
所以比例=3/8

（2）设税前为X，则12000=X-tax=X-10%（X-3000)，解方程即可

（3）R和S每小时单独做的工作量之和等于R和S合作时的每小时工作量，设S单独工作s小时能完成工作，则：
1/9+1/s=1/6，解方程即可。