Question: Under standard growth conditions, the bacterial strain, E.coli, has a doubling time of 20 minutes.  If 1 single bacterial cell is used to start a culture grown under standard growth conditions, how many bacterial cells will there be after the culture is grown for 4 hours?
Answer with step-by-step thinking: 4 hours is 4 * 60 = 240 minutes. If the doubling time is 20 minutes, then after 240 minutes, the number of bacteria would have doubled 240 / 20 = 12 times. Thus, starting with only 1 bacterial cell, after 4 hours, there will be 1 * 2 * 2 * 2 * 2 * 2 * 2 * 2 * 2 * 2 * 2 * 2 * 2 = 4,096 bacterial cells.
So the answer is 4096.


Question: Karen is considering her winter coat options. One coast costs $300 and will last for 15 years. The other coat costs $120 and will last for five years. How much money would Karen save over 30 years by buying the more expensive cost?
Answer with step-by-step thinking: First find the number of cheaper coats Karen will have to purchase over 30 years: 30 years / 5 years / coat = 6 coats. Then multiply that number by the cost of one cheaper coat to find the total cost of that option: 6 coats * $120 / coat = $720. Then find the number of more expensive coats Karen will have to purchase over 30 years: 30 years / 15 years / coat = 2 coats. Then multiply that number by the cost of one expensive coat to find the total cost of that option: 2 coats * $300 / coat = $600. Then subtract the total cost of the more expensive coats from the total cost of the less expensive coats to find the difference: $720 - $600 = $120.
So the answer is 120.


Question: Carson is going to spend 4 hours at a carnival. The wait for the roller coaster is 30 minutes, the wait for the tilt-a-whirl is 60 minutes, and the wait for the giant slide is 15 minutes. If Carson rides the roller coaster 4 times and the tilt-a-whirl once, how many times can he ride the giant slide? (Wait times include the time actually spent on the ride.)
Answer with step-by-step thinking:
First figure out how many minutes Carson spends at the carnival by multiplying the number of hours he's there by the number of minutes per hour: 4 hours * 60 minutes / hour = 240 minutes. Then figure out how long Carson spends waiting for the roller coaster by multiplying the wait time per ride by the number of rides: 4 rides * 30 minutes / ride = 120 minutes. Now subtract the time Carson spends on the roller coaster and tilt - a - whirl from the total time he spends at the park to find out how much time he has left: 240 minutes - 120 minutes - 60 minutes = 60 minutes. Now divide the time Carson has left by the wait time for the giant slide to see how many times he can ride it: 60 minutes / 15 minutes / ride = 4 rides.
So the answer is 4.