3 years ago

Use a 10-by-10 grid to solve. What percent of 400 is 20?

Mathematics

1 answer:

Lostsunrise [7]3 years ago

6 0

The correct answer is 5%.

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2 years ago

If the radioactive half-life of a substance is 20 days, and there are 5 grams of it initially. When will the amount left be 2 gr

Kobotan [32]

Answer: $26.4\ \text{days}$

Step-by-step explanation:

Given

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$\Rightarrow A=A_o2^{\dfrac{-t}{T_{\frac{1}{2}}}}\\\\\Rightarrow 2=52^{\dfrac{-t}{20}}\\\\\Rightarrow 0.4=2^{\dfrac{-t}{20}}\\\\\Rightarrow 2^{\dfrac{t}{20}}=2.5\\\\\Rightarrow \dfrac{t}{20}\ln 2=\ln (2.5)\\\\\Rightarrow t=\dfrac{20\ln (2.5)}{\ln 2}\\\\\Rightarrow t=26.4\ \text{days}$