The half-life of 42K is 12.4 hours. How much of a 750.0-gram sample is left after 62.0 hours?

23 g

Explanation:

Amountafter = Amountbefore * (1/2)^(t/thalf)

Amountafter = (750 grams) * (1/2)^(62.0 hours/12.4 hours)

Amountafter = 23.4375 grams

750 has 2 significant digits

12.4 and 62.0 have 3 significant digits

So we take the lower of 2 significant digits:

23 grams

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