posted by micky .
an original sample of K-40 has a mass of 25.00 grams. After 3.9x 10 to the ninth years, 3.125 grams of the original sample remains unchanged. What is the half-life ok K-40 in minutes?
Is it 6.8328 x 10 to the 14th
Yes but you are allowed only 2 significant figures so you should round to 6.8E14 min.