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Bunuel
A culture of bacteria had a population of 8,000 at 10 AM. The population grew at a fixed percentage rate per hour and reached 64,000 at 7 PM on the same day. If the population continues to grow at that same rate, at what time will the population reach 256,000?

A. 9 PM of the same day
B. 10 PM of the same day
C. 12 AM of the next day
D. 12:30 AM of the next day
E. 1 AM of the next day

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This is exponential growth. The stem gives us:

\(8000*k^9=64,000\)

Simplifying, we get for equation 1:
\(k^9=8,000=2^6*5^3\)

We are looking for:
\(8,000*k^n=256,000\). Simplified down, that's \(k^n=2^8*5^3\) which we'll use as equation 2.

Comparing the two, we can see that the factor of 2 is what changed here, not the factor of 5. That helps us with identifying k. In equation 1, we can divide the exponent of k by the exponent of 2 to find the growth factor, which is \(\frac{3}{2}\).

Great, let's sub this into equation 2 now. We're looking for a value n that divided by 8, gives us 3/2.

\(\frac{n}{8}=\frac{3}{2}\)

Thus, \(n=12\). 12-9=3, so 3 hours later, which puts us at 10pm on the same day. Thus B is the answer.
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8000 at 10 AM
64000 at 7 PM

Equation as per per question:
8000 * x^9 = 64000
x^9 = 8
x^3 = 2
This implies in 3 hours, the population is getting doubled.

So if at 7 pm, it is 64000
then at 10 pm, it will become 128000
and at 1 am, it will become 256000

Hence (E) is the answer
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Bunuel
A culture of bacteria had a population of 8,000 at 10 AM. The population grew at a fixed percentage rate per hour and reached 64,000 at 7 PM on the same day. If the population continues to grow at that same rate, at what time will the population reach 256,000?

A. 9 PM of the same day
B. 10 PM of the same day
C. 12 AM of the next day
D. 12:30 AM of the next day
E. 1 AM of the next day

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64000 = 8000 (1+r/100)^9

8 = (1+r/100)^9

2^3 = (1+r/100)^9

(1+r/100)^3 = 2

256,000 = 8000 * 32

= 8000 * 2^5

= 8000*((1+r/100)^3)^5

= 8000(1+r/100)^15

10 am + 15 hours = 1 am next day

Option E
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8000 to 64000=8 ( the population multiplies by 8) = 2^3
10a.m to 7.pm= 9hrs difference = 3^2
so it means the population increases twice after every 3 hrs
7p.m to 10 p.m the population was 64000 x 2= 128000 (3hrs difference)
10p.m to 1.am the population was 128000 x 2= 256000 (3hr difference)
So the population will be 256000 at 1.am next day

Correct answer is E
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In 9 hours, it went from 8,000 to 64,000, which is 8,000*8
Therefore increase in 9 hours = 8x units (64,000/8,000 = 8) where x = original population
Hence for it to go from 64,000 to 256,000
We need 256,000/64,000 = 4x units = 8x/2

Hence, we need 9/2 = 4.5 hours
Answer = D = 12:30AM


Bunuel
A culture of bacteria had a population of 8,000 at 10 AM. The population grew at a fixed percentage rate per hour and reached 64,000 at 7 PM on the same day. If the population continues to grow at that same rate, at what time will the population reach 256,000?

A. 9 PM of the same day
B. 10 PM of the same day
C. 12 AM of the next day
D. 12:30 AM of the next day
E. 1 AM of the next day

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given at 10 AM ---total 8000 bacteria count , which increases at a constant percentage growth per hour let x% per hour so the multiplying factor per hour is (1+x/100)
now at 7 PM i.e. in 9 hours this count increases to 64000
i.e. 8000*(1+x/100)^9=64000
(1+x/100)^9=8=2^3
(1+x/100)^3=2-------i
now let in 'n' hours the count reaches to 256000
i.e. 64000(1+x/100)^n=256000
(1+x/100)^n=4=2^2
from i, (1+x/100)^n=(1+x/100)^6
n=6 hrs so at 01 AM the value of bacteria reaches 256000 count
so E
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using the values w/o 000 & it's a GP

final = initial*r^t
64 = 8r^9
8 = r^9
r = 8^1/9
r = 2^3/9 = 2^1/3

now

256 = 8r^t
32 = 2^1/3t
2^5 = 2^1/3t

this implies

5 = 1/3t & t = 15hrs, counting the time, it would be 1AM

Ans E
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Bunuel
A culture of bacteria had a population of 8,000 at 10 AM. The population grew at a fixed percentage rate per hour and reached 64,000 at 7 PM on the same day. If the population continues to grow at that same rate, at what time will the population reach 256,000?

A. 9 PM of the same day
B. 10 PM of the same day
C. 12 AM of the next day
D. 12:30 AM of the next day
E. 1 AM of the next day

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Population at 10 Am = 8000
Population at 7 pm = 64,000
population at ? = 256,000

10 am to 7 pm = 9hr

8000*(x)^9 = 64000
x^9 = 8
x = 2^(1/3)

8000*(Z) = 256000
z=2^(5)

so to get to 256000 from 64,000 time required :
2^(t/3) = 2^(5)
t = 15 hr

so 15 hrs from10 am is 1 am next day; E is the answer
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Bunuel
A culture of bacteria had a population of 8,000 at 10 AM. The population grew at a fixed percentage rate per hour and reached 64,000 at 7 PM on the same day. If the population continues to grow at that same rate, at what time will the population reach 256,000?

A. 9 PM of the same day
B. 10 PM of the same day
C. 12 AM of the next day
D. 12:30 AM of the next day
E. 1 AM of the next day

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Lets consider a geometric progression
a,ar,ar1,...ar9....ar^(n)
a=8000
ar9=64000
r=2^(1/3)
ar^n=256000
8000x( 2^1/3)^n= 256000
n=15
10 am + 15 hours = 1 am
ans-E

But question seems little vague
is 64000= in 10th terms or sum of all 10 terms.....had a little doubt in how to clear this vagueness in wordings
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Rate of growth over 9 hours = 64,000/8,000 = 8

(rate) ^ 9 = 8
(rate) ^ 9 = 2^3

(rate)^ 3 = 2 -------(i)


Let x be hours after 10AM when population will be 256,000.

So, 8000 (rate) ^ x = 256000

(rate) ^ x = 32
(rate) ^ x = 2 ^ 5 ------- (ii)


from (i) and (ii) ,
x = 3 * 5 = 15

So, population will be 256000 15 hours after 10 AM which is 1 AM next day.

Answer E
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8000 @ 10am to 64000 @ 7pm is an increase of 8 or 2^3 in 9 hours. This essentially means that every 3 hours, the number doubles.

So I counted from 7pm and doubled the figure every 3 hours.

7pm = 64000
10pm = 128,000
1pm = 256,000
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0. Read the question twice
1. Understand what your data has

8000 at 10 AM=10.00
64.000 at 7PM=19.00
256.000 at ___?

2. Simplify and look at similarity

8 -> 2^3
64 -> 2^6
256 -> 2^8

8 to 64 in 9 hours (19.00-10.00), meaning 2^3 in 9 hours ~ x^2 in each 3 hours

3. So, we can run simulations below

8 [b]10am[/b]
(8x2)16 1 pm
(16x2) 32 4 pm
(32x2) 64 @ 7 pm
(64x2) 128 10 pm
(128x2) 256 [b]1 am [/b]

So, the answer is E. 1 AM of the next day



Bunuel
A culture of bacteria had a population of 8,000 at 10 AM. The population grew at a fixed percentage rate per hour and reached 64,000 at 7 PM on the same day. If the population continues to grow at that same rate, at what time will the population reach 256,000?

A. 9 PM of the same day
B. 10 PM of the same day
C. 12 AM of the next day
D. 12:30 AM of the next day
E. 1 AM of the next day

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answer E

when from 8000 to 64000 in 9 hours
8x larger in 9 hours is 2^3 in 9 hours, doubling time is 3 hours

to get to 256,000 is will take 6 hours, 2 more doubling times from 64,000 to 256,000

Bunuel
A culture of bacteria had a population of 8,000 at 10 AM. The population grew at a fixed percentage rate per hour and reached 64,000 at 7 PM on the same day. If the population continues to grow at that same rate, at what time will the population reach 256,000?

A. 9 PM of the same day
B. 10 PM of the same day
C. 12 AM of the next day
D. 12:30 AM of the next day
E. 1 AM of the next day

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Solution:

At 10:00 AM = 8000(Population)

Reaches at 7:00 PM = 64000

So, if we we sum up 64000 for every hour the population would reach at 256000 at 10PM of the same day.

Answer Option B


Bunuel
A culture of bacteria had a population of 8,000 at 10 AM. The population grew at a fixed percentage rate per hour and reached 64,000 at 7 PM on the same day. If the population continues to grow at that same rate, at what time will the population reach 256,000?

A. 9 PM of the same day
B. 10 PM of the same day
C. 12 AM of the next day
D. 12:30 AM of the next day
E. 1 AM of the next day

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Answer is 1am next day. Find the solution in attached pic
Attachments

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1000005448.jpg [ 54.99 KiB | Viewed 315 times ]

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Bunuel
A culture of bacteria had a population of 8,000 at 10 AM. The population grew at a fixed percentage rate per hour and reached 64,000 at 7 PM on the same day. If the population continues to grow at that same rate, at what time will the population reach 256,000?

A. 9 PM of the same day
B. 10 PM of the same day
C. 12 AM of the next day
D. 12:30 AM of the next day
E. 1 AM of the next day

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The population at 7pm: 64,000
We want to find at what time the population will be 256,000

i.e, at what time the population will be 256000/64000= 4 times of what it is at 7pm.

Now, from 10am to 7pm there is a nine hour difference:
Population grew : 64000/8000 by 8 times which is 2^3.
i.e, it doubled every 3 hours.

=> To make it 4times of the population at 7pm we need 6 hours.
So the time will be 1AM next day.

Answer: E
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10 AM - 8000
7 PM - 64000

Duration = 9 hours
Let growth factor = a

=> 64000 = 8000 * a^9
=> 8 = a^9
=> 8^(1/9) = a

Final target = 256000
Let the time be 'n' hours
=> 256000 = 8000*a^n
=> 32 = a^n
=> 32 = [8^(1/9)]^n
=> 2^5 = 2^(n/3)
Equating both sides we get
5 = n/3
=> n = 15 hours

Calculating 15 hours from 10 am = 1 AM

Option E

Bunuel
A culture of bacteria had a population of 8,000 at 10 AM. The population grew at a fixed percentage rate per hour and reached 64,000 at 7 PM on the same day. If the population continues to grow at that same rate, at what time will the population reach 256,000?

A. 9 PM of the same day
B. 10 PM of the same day
C. 12 AM of the next day
D. 12:30 AM of the next day
E. 1 AM of the next day

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