1. A chemist needs to create a 45% HCl solution. (HCl is hydrochloric acid. A "45% HCl solution" contains 45% HCl and the other 55% is water.) How much of a 80% HCl solution must be mixed with 55 ml of a 35% HCl solution in order to result in a 45% HCl solution? Round your answer to 2 places after the decimal point (if necessary) and do NOT type any units (such as "ml") in the answer box.

2. Duan leaves school to walk home. His friend, Valentina, notices 0.1 hours later that Duan forgot his phone at the school. So Valentina rides her bike to catch up to Duan and give him the phone. If Duan walks at 4.2 mph and Valentina rides her bike at 11 mph, find how long (in hours) she will have to ride her bike until she catches up to him. Round your answer to 3 places after the decimal point (if necessary) and do NOT type any units (such as "hours") in the answer box. Time for Valentina to catch up to Duan: hours

3. the bank loaned out $2800, part of it at a rate of 8.9% per year and the rest of it at a rate of 5% per year. The total amount of interest owed to the bank at the end of one year was $170.36. Find the amount of money that the bank loaned out at 8.9%. Round your answer to the nearest cent (2 places after the decimal point), and do NOT type a dollar sign in the answer box. Amount of money loaned at 8.9%: $?

4.

Jane can sand and refinish the hardwood floor in a certain room in 25 hours. Together with her co-worker, Alex, they can sand and refinish this room's floor in 20 hours. How many hours would it take Alex working by himself to sand and refinish this floor? Round your answer to 2 places after the decimal point (if necessary) and do NOT type any units (such as "hours") in the answer box. Time for Alex to sand and refinish this floor: ....... hours