Chapter 1 - First-Order Differential Equations - 1.1 Differential Equations Everywhere - Problems - Page 13: 33

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Given: $M=280g\\ a=0.25\\ m_0=8g$ 75% of its fully grown size means $m=280\times\frac{75}{100}=210$ Obtain: $210=(280)[1-(1-\frac{8}{280}^{\frac{1}{4}})e^{\frac{-0.25t}{4(280)^{\frac{1}{4}}}}]^4 $ Solve for $t$ we have: $t=240$ Hence, it will take240 days for the rat to reach 75% of its fully grown size