Since

W

=

1 t - 4 t2 ,

The rate of change of W is given by

dW dt

=

- 1 t2 + 8 t3 .

Evaluating this at time t = 10 seconds gives

dW dt = - 1 100 + 8 1,000

=

- 0.002 kg. per second.

Since this is a negative rate of change, we conclude that the amount of rocket fuel is decreasing at a rate of 0.002 kg. per second.

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