1. It takes 12 hours for Party A to make a box of toys, and 8 hours for Party B to make a box of toys. Two people cooperate to make a box of toys, and Party B makes a box of 42 toys. Q: How many toys are there in this box?

1/ 12+ 1/8=5/24

1/(5/24)=24/5

1/8*24/5=3/5

42/(3/5)=70

There are 70 toys in this box.

2. A vendor bought 1000 live crabs at the price of each 20 yuan. He sells live crabs in the market at the price of each 25 yuan and dead crabs at the price of each 5 yuan. After selling it all, he earned 3000 yuan. What is the mortality rate of these dead crabs?

1000*5=5000 (yuan)

5000-3000=2000 (yuan)

2000/( 15+5)= 100 (yuan)

100/ 1000= 10%

A: The mortality rate of these dead crabs is 10%.

3. The personal income tax rate in a certain period is: monthly income1.below 500 yuan, the part between 1.500 yuan and 2000 yuan is taxed at 5%, and the part between 2000 yuan and 3000 yuan is taxed at 10%. Xiao Liu's actual monthly income at that time was 2250 yuan. How much personal income tax should he pay every month?

500*5%=25 (yuan)

250* 10%=25 (yuan)

25+25=50 yuan.

He should pay 50 yuan personal income tax every month.