Krypton-85 has a half-life of 10.76 years. It decays into rubidium-85. Suppose a sample contains 4 atoms of krypton-85 and 12 atoms of rubidium-85.
About how old is the sample?
A. 10.76 years
B. 21.52 years
C. 43.04 years
D. 32.28 years

see the picture for the vector

the magnitude of the vector by pythagorean theorem

r = √( (-10)^2 + (3)^2 ) = √109

magnitude = √109 units

the direction angle between vector and x-axis is

tan^(-1)(3/10) = 16.699

so the direction is approximately 16.7 degrees north of west

blue light is scattered in different directions by the tiny molecules of air. blue is scattered more than other colours because it has a shorter distance to travel which results in smaller waves. this is why we see a blue sky most of the time.