BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Exp growth

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
Senior | Next Rank: 100 Posts
Posts: 58
Joined: Thu Jul 22, 2010 5:40 pm
Thanked: 1 times

Exp growth

by Jinglander » Fri Aug 20, 2010 9:13 pm
can someone explain how to solve questions like these. I am looking both for a general strategy and a solution.

The answer is sqrt(2)

A strain of bacteria mulitplies such that the ratio of its population in any two consectuive minutes is constant. If it grow from a population of 5 mil to a pop of 40 mil in 1 hour, by what factor does the population increase in 10 minutes
Top
Source: — Problem Solving |
User avatar
Master | Next Rank: 500 Posts
Posts: 307
Joined: Sun Jul 11, 2010 7:52 pm
Thanked: 36 times
Followed by:1 members
GMAT Score:640

by limestone » Fri Aug 20, 2010 9:38 pm
If the pop is double after a period then pop is
2 folds after 1 period
2^2 folds after 2 periods
2^3 folds after 3 periods
.......
(original pop factor is 1)
The pop of bacteria increases 8 folds after 60 minutes ( 40/5 =8). Now if one period is 10 minutes we have 6 periods here.
The same rule as above:
x^6 = 8 = 2^3
x^2 = 2, then x = sqrt(2)

Another example, if I take 20 minutes as a period, I have 3 periods here, and
x^3 = 8, x = 2
if a period is 30 minutes, x^2 = 8, then x = 2 * sqrt(2)

Hope this can help.
Top
Post new topic Post Reply
• Page 1 of 1