if 90% of the microbes are killed every 10 minutes, what percentage is still alive after 20 minutes?

Answer 1

Exponential decay equation:

y = A(R)^(x/t)

Where:

y = total units (microbes, in your case) at time point x
A = intial amount
R = rate of decay (expressed as a decimal of the "amount left," so for you it's "10% left after decay" or 0.10).
x = specific time
t = time it takes for the decay rate to complete one cycle

So for you, you have your x, R and t. Since the question only wants a percentage, you don't have to worry about total or inital amounts. For percentage's sake, lets say you started with 100 (100%). Basically I just changed the units from microbes to percentages.

So:

y = 100(0.10)^(x/10)
y = 100(0.10)^(20/10)
y = 100(0.10)²
y = 100(0.01)
y = 1

One percent are left.

Answer 2

Say you have 100 microbes. If 90% are killed in 10 minutes, you have 10 left. In 10 more minutes, 90% of the remaining microbes are killed, so you would have 1 left.

So all in all, after 20 minutes, you'd have 1% left.

Answer 3

90% killed equals 10% alive.

So, at 10 minutes, 10% survive.
And, after another 10 minutes, 10% of 10%, or 1% are alive.

Answer 4

10%

Answer 5

you would have 10% of the 10% left, you need to know how much was there originally though!

Answer 6

Depends on the growth rate....E.coli doubles every 20 minutes, for example....

Answer 7

140%

Answer 8

one percent

Answer 9

1.0%...m i right??? :-?