The half-life for a 400-gram sample of radioactive element X is 3 days. How much of element X remains after 15 days have passed? A.
12.5 g

B.
25 g

C.
50 g

D.
100 g

compass can be used day and night, cloudy or sunny

answer: 2×10^-2kg

explanation: density= mass per volume

vol=mass/density

converting to s.i units we have;

3÷1000kg = 0.003

1.5÷100m = 0.15

0.003/0.15 = 0.02kg

r = ρ x length / area  

ρ = r x area / length  

ρ is in ohm-meters  

in basic units, it is m³kg/s³a²  

i think this is it.