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chaitanya.mehrotra: Master | Next Rank: 500 Posts; Posts: 184; Joined: Thu Nov 25, 2010 9:57 pmFollowed by: 5 members; Thanked: 1 times; GMAT Score:700

by chaitanya.mehrotra » Mon Aug 08, 2011 7:13 am

The half-life of a radioactive isotope, or form of a chemical element, is defined as the time
required for the number of radioactive atoms present to fall by half.

(a) Write the formula for the number of radioactive atoms present after t minutes, if
you start with 106 radioactive atoms and the half-life is 18 minutes.

(b) After 3 hours, approximately how many radioactive atoms are remaining? Use the
formula you derived previously.

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Source: Beat The GMAT — Problem Solving | Mon Aug 08, 2011 7:13 am

gmatboost: Master | Next Rank: 500 Posts; Posts: 312; Joined: Tue Aug 02, 2011 3:16 pmFollowed by: 33 members; Location: New York City; Thanked: 130 times; GMAT Score:780

by gmatboost » Mon Aug 08, 2011 7:49 am

This is pre-calculus, you won't see this question on the GMAT.

The answer goes something like this:

A. Final = 106 * (1/2)^(t/18)

B. Final = 106 * (1/2)^(180/18) = 106 * (1/2)^(10) = 106 * (1/1024) = 106/1024 = 53/512

Note that as far as I am aware, this doesn't make sense, since you must have an integer number of atoms. (I am not a scientist.)

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aditi2013: Newbie | Next Rank: 10 Posts; Posts: 1; Joined: Fri Nov 23, 2012 9:45 pm

by aditi2013 » Sat Nov 24, 2012 11:12 pm

gmatboost wrote:This is pre-calculus, you won't see this question on the GMAT.

The answer goes something like this:

A. Final = 106 * (1/2)^(t/18)

B. Final = 106 * (1/2)^(180/18) = 106 * (1/2)^(10) = 106 * (1/1024) = 106/1024 = 53/512

Note that as far as I am aware, this doesn't make sense, since you must have an integer number of atoms. (I am not a scientist.)

Well the question was 10^6 (10 raised to the power of 6) I know its very old post, but wanted to see if this concept really needs to be studied.

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