Law of Poiseuille : $F = kR^4$ French physiologist Jean Louis Poiseuille denoted the amount of blood at unit time in the blood vessel as below : $$F = kR^4$$ $F$ : Amount of Flood of Blood $R$ : Radius of Blood Vessel When $R$ increases 7%, how much would $F$ be increased? * * * **my solution** $dF/dR = 4kR^3$ thus, $4k(1.07)^3 $ Is it correct?

Its right till you dont plug in the values. A way can be take logs in your original equation . This gives us $\ln (F)=\ln (k)+4\ln (R) $ differentiating we have $\frac {dF}{F}=\frac {4dr}{R} $ now multiplying by $100$ we have $\text {percent change in F}=4×7=28\text {percent} $