• October 19th 2012, 08:42 AM
hisajesh
f(0)= 24 and f(4)= 20. Its speed has been "diminished" by 4 and that is $k\sqrt{4}= 2k= 4$ so that k= 2. $24- k\sqrt{n}= 24- 2\sqrt{n}= 0$ gives $\sqrt{n}= 12$ which gives MaxJasper's answer.