A scientist models the number of grams of a radioactive substance with the expression 15. (2)/5, where d is the number of days since the sample was measured.

1. After 20 days, will there be more or less than 1 gram of the substance left? Explain your reasoning

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.