A super-deadly strain of bacteria is causing the zombie population to double every 2 days. Currently, there are 25 zombies. After how many days will there be 25,600 zombies?

Question

A super-deadly strain of bacteria is causing the zombie population to double every 2 days.  Currently, there are 25 zombies.  After how many days will there be 25,600 zombies?

psirockin2 · Answer

Okay so... it's increasing by double every 2 days

psirockin2 · Answer

8 days

shaleiah · Answer

how did you get 8 days?

shaleiah · Answer

@psirockin2

amorfide · Answer

25, 50, 100, 200, 400,...., 25600

you have a common ratio of 50/25=100/50=200/100 etc so r=2
geometric sequence is a, ar, ar^2, ar^3
so you want ar^n=25600
our first term is 25, r=2, so 
$$25(2^{n})=25600$$

princeharryyy · Answer

that's a GP. Geometric progression.

amorfide · Answer

please not that for a geometric sequence

a,ar,ar^2,....,ar^n is the standard form for it
a is the first term of the sequence 
r is the ratio

to get the ratio, r, you would divide 2 consecutive terms

ar/a=ar^2/ar=ar^3/ar^2, etc

sorry I thought I would clarify just incase

princeharryyy · Answer

@amorfide don't u thing u might still be wrong.

princeharryyy · Answer

day 0 no. of bacteria = 25
after 2 days bacteria's = 50
after another 2 days bacteria's = 100
after another 2 days bacteria's = 200
after another 2 days bacteria's =400
after another 2 days bacteria's =800
after another 2 days bacteria's =1600
after another 2 days bacteria's =3200
after another 2 days bacteria's =6400
after another 2 days bacteria's =12800
after another 2 days bacteria's 28600

total days add all the days. 2*10 = 20

princeharryyy · Answer

your aren't wrong, that's a GP only.

amorfide · Answer

ah, yeah, sorry

princeharryyy · Answer

@amorfide

princeharryyy · Answer

the only problem with that is it's not after every day that's after every two days.

princeharryyy · Answer

so, u wud have to keep in mind of that while solving that. otherwise it's perfect np.

amorfide · Answer

so since I treated the progression as per day, I should multiply the answer by 2, so no problem. Thank you for correcting

princeharryyy · Answer

yeah. that's what I am saying :)

amorfide · Answer

I will rewrite it for the op

shaleiah · Answer

I'm looking for the growth rate formula

amorfide · Answer

no idea what that is

princeharryyy · Answer

@amorfide gave u the formula. but u wud have to keep in mind of the days.

princeharryyy · Answer

that's rate only.

amorfide · Answer

I can't help
@princeharryyy  please would you be so kind

shaleiah · Answer

@563blackghost