Solve the problem.A certain radioactive isotope has a half-life of approximately 1900 years. How many years to the nearest year would be required for a given amount of this isotope to decay to 20% of that amount? Round to the nearest year.
A. 612 yr
B. 4392 yr
C. 4412 yr
D. 1520 yr
Answer: C
Mathematics
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Convert the percent to a fraction.3.55%
A. 
B. 
C. 
D. 
Mathematics
Use a proportion to solve the problem.A math teacher claims that the students' test scores are directly proportional to the amount of time spent studying. Amy studies 14 hours for a test and gets a score of 70. At this rate, how many hours would she have to study to get a score of 83?
A. 27 hr B. 16.6 hr C. 17.43 hr D. 11.81 hr
Mathematics
Find the hours, rate, or earnings as specified.
Find the gross earnings for the week. Overtime hours are any hours over 40.
A. $1,214.55 B. $854.55 C. $809.55 D. $1,169.55
Mathematics
Simplify.3 ? {(300 - 85 รท 5) - [3 ? 21 - (8 - 2 ? 3)]}
A. 2442 B. 616 C. 666 D. -834
Mathematics