Question

An 80 gram sample of a radioisotopes decayed to 40 grams in 3 days how many grams of the original sample would remain after 9 days

Answer 1

Answer: 10 grams

Explanation: Original sample is 80 gram and every three days half of its composition decays so 80 down to 40 in the first 3 days, 20 in the next three days, and  10 in the last three days