Math Minute Answers – Week 3

Congratulations to Brittany, the winner of last week’s Math Minute. Enjoy your Adopt-a-Microbe T-shirt! Here are the answers to last week’s questions. Monday’s question is up on the expedition page, so if you didn’t win last week, keep calculating!

Monday: It’s Hump Day…the halfway mark of our expedition! There are 31 days left (including today) and we work 12 hours per day. I wonder how many hours we have left to work?

31 days x 12 hours/day = 372 hours

We had 372 hours left on hump day. If we worked 8-hour days, 5 days a week, that would be just over 9 weeks worth of work!

Tuesday: The pipe we use for the drill string weighs about 28 pounds a foot, and each stand of pipe is 30 meters long. If the whole string is 150 stands long, how much does it weigh?

28 lbs/ft x 3.28 ft/1 m = 91.84 lbs/m

150 stands x 30 m/stand = 4500 m

91.84 lbs/m x 4500 m = 413,280 lbs

The drill string weighs approximately 413,280 pounds; almost 207 tons.

Wednesday: We started with 1,285 cartons (dozens) of eggs, and we’ve now been at sea for 32 days. If each person eats, on average, 2 eggs a day, how many eggs have we used (remember there are 120 people on board)? Do you think we’ll have enough to last?

120 people x 2 eggs/person/day x 32 days = 7,680 eggs used

1285 eggs x 12 eggs/dozen = 15,420 eggs

15,420 eggs total – 7,680 eggs used = 7,740 eggs left

We used 7,680 eggs for half the cruise, and we have 7,740 left, so we should have enough!

Thursday: Microbiologists use a solution of 70% ethanol in water to sterilize their equipment. How much ethanol do they need to make up 500 mL of sterilizing solution for each of 8 microbiologists?

500 mL x 8 people = 4000 mL

70% = 0.70

4000 mL x 0.70 = 2800 mL of ethanol

They will need 2800 mL—or 2.8 L— of ethanol to make up their sterilizing solution.

Friday: When we pump cement into the hole to stabilize the casing, the pump rate is 0.117 barrels per stroke. If we pump at a rate of 60 strokes per minute, how long will it take to pump 20 barrels of cement?

0.117 barrels/stroke x 60 strokes/min = 7.02 barrels/min

20 barrels ÷ 7.02 barrels/min = 2.85 min

It will take 2.85 minutes—or 2 minutes, 51 seconds—to pump the 20 barrels of cement.