# maths

The mass of a particular substance is known to grow exponentially at a rate of 0.5% per hour. Its initial mass was 25 grams and, after t hours, it weighed 31 grams.

The equation modelling this growth is

25×1.005 t  =  31.

Use the method of taking logs to solve this equation for t, giving your answer correct to the nearest hour.

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asked by Grace
1. Your equation is incorrect, it should say

25(1.005)^t = 31
then
1.005^t = 1.24
log (1.005^t) = log 1.24
t(log 1.005) = log 1.24
t = log 1.24/log 1.005 = appr. 43.1 hrs

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posted by Reiny
2. Oh sorry! Thanks

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posted by Grace

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