Answer:
3 minute 35.969420299997999 seconds
Step-by-step explanation:
Okay in simple words its 3 minute and 35 seconds or something.
Since we want to leave 2 grams ,
Amount to decay = 680-2
= 678g
Amount decayed per minute = 27.7 %
Amount decayed per minute ( in grams) = 188.36 g
Amount decayed per second ( in gram ) = 3.139333333g
Your required Ans = 678 / 3.139333333
= 215.9694203 seconds
i have converted them to minute in the title : D