A radioactive substance decays at a rate of y = ae-0.1483, where tin in hours. Find the half-life of the substance.
t= 0.8622 years
t = 4.674 years
t = 18.323 years
t = 0.1028 years

White shapes and black shapes are used in a game. some of the shapes are circles. while the rest are squares. the ratio of the number of white shapes to the number of black shapes is 5: 11. the ratio of the number of white cicrles to the number of white squares is 3: 7. the ratio of the number of black circles to the number of black squres is 3: 8. work out what fraction of all the shapes are circles.