1. Students enrolling in a private tutoring program must first take a placement test that costs $35. They can then receive tutoring at the cost $18.50 per hour. If you set aside $350 to get extra help, how many hours of tutoring can you afford?

2. You wake up one morning with a wad of cash in your pocket, consisting entirely of $50 and $100 bills. You remember that between the 50's and the 100's you have a total of 30 bills with a total value of $2500. How many $50 bills do you have? How many $100 bills do you have?

3. A contractor requires a mix that is 70% sand and 30% cement by mass. He starts off with 1400 kg of a mix that is 80% sand and 20% cement. How much cement should he add so that he gets the required mix?

4. You have a jar of loose change which contains pennies, nickels, dimes, and quarters. The total value of the change in the jar is $104. In total, there are exactly 1000 coins in the jar. There are four times as many pennies as there are nickels and there are twice as many pennies as there are dimes. How many of each type of coin are there?