Answer:
Explanation:
Given
half life 
billion year
10 % to decay i.e. 90 % remaining
And 
where k= constant
t=time
and 
so 
t=0.684 billion year
(b)
t=13.8 billion year
atoms
85 + 45 = 130
130km in 1.5 hours
130 / 1.5 = 86.6666666666666
the average speed was:
86.6666666666666
a brainliest would be appreciated
Answer:
Density, mass of a unit volume of a material substance. The formula for density is d = M/V, where d is density, M is mass, and V is volume. Density is commonly expressed in units of grams per cubic centimetre. ... Density can also be expressed as kilograms per cubic metre (in metre-kilogram-second or SI units).
The density of water is about 1 g/cm3, since the gram was originally defined as the mass of one cubic centimetre of water at its maximum density at 4 °C.
