Answer:
Amount of radioactive particles left after 60 years = 100 particles.
Explanation:
Amount of radioactive particles before 60 years = 400
Amount of radioactive particles present today = 200
That is radio active particles reduced to half. That is 60 years is half life of this radio active material.
After 60 years this 200 radio active particles will reduce to half.
Amount of radioactive particles left after 60 years = 0.5 x 200 = 100 particles.
