Posted by **edward** on Saturday, November 24, 2012 at 4:07am.

a circular ink-blot grows at a rate of 2 sq cm per second. find the rate at which the radius is increasing after (28/11)seconds.

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**Steve**, Saturday, November 24, 2012 at 4:55am
assuming it had zero area at t=0,

a = pi r^2

da/dt = 2pi r dr/dt

2 = 2pi (28/11) dr/dt

11/(28pi) = dr/dt

- maths -
**edward**, Saturday, November 24, 2012 at 7:12am
i tried this way but answer not coming..... :/

ans is 0.25

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**Steve**, Saturday, November 24, 2012 at 10:39am
nope. I don't buy it. I think the answer lost a factor of 2 somewhere. 11/(28pi) is 0.125

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