The mass of a an atom of helium is 6.65 x 10^−24. use scientific notation to express the mass of 250 helium atoms. a) 1.6625 x 10−21 b) 1.6625 x 10−22 c) 1.6625 x 10−24 d) 1.6625 x 10−26

i took the test and it's actually A)1.6625 x 10−21 :)

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  (a) 48π cm²/min ≈ 150.80 cm²/min

  (b) 288π cm²/min ≈ 904.78 cm²/min

Step-by-step explanation:

The area of a circle of radius r is given by the formula ...

  A = πr²

Then the rate of change of area is ...

  A' = 2πr·r'

For the given rate of change of radius, this will be ...

  A' = 2πr·(4 cm/min) = 8πr cm/min

When r = 6 cm, the rate of change of area is ...

  A' = 8π(6 cm) cm/min = 48π cm²/min ≈ 150.80 cm²/min

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When r = 36 cm, the rate is ...

  A' = 8π(36 cm) cm/min = 288π cm²/min ≈ 904.78 cm²/min