Answer: 956 years * log2(2)
Explanation:
The half-life of the substance is 956 years, which means that every 956 years the amount of substance is reduced by half. Therefore, the ratio of the initial amount to the final amount is 2:1. To find out how many half-lives it takes for 700 grams of substance to decay to 350 grams, we need to find the logarithm base 2 of this ratio:
log2(2:1) = log2(2) = 1
This means that one half-life has passed. Since the substance decays from 700 grams to 350 grams in one half-life, it must have decayed from 1400 grams to 700 grams in two half-lives. Therefore, it takes two half-lives, or 1912 years, for 700 grams of the substance to decay to 350 grams.