# Math Help - Growth & Decay

1. ## Growth & Decay

Hi

Could someone please show me why I cant get the right answer for (c) which is 76.07???

2. Originally Posted by UltraGirl
Hi

Could someone please show me why I cant get the right answer for (c) which is 76.07???
1. All your considerations and calculations are correct - except the very last line: You used an incomplete value of k in the exponent.

2. With
$k=-\frac2{35} \ln\left(\frac{13}{28}\right)$
and
$t = 20$

you'll get:

$T_1=64+56 \cdot e^{-\frac74 \cdot -\frac2{35} \ln\left(\frac{13}{28}\right) \cdot 20}$

which simplifies to

$T_1=64+56 \cdot e^{2 \ln\left(\frac{13}{28}\right)} = \frac{1065}{14}\approx 76.0714...$