How much of a radioactive substance must be presented to decay to 40 grams in 9 years if the half-life of the substance is 4.6 years?
Between 140 and 145 grams
Between 145 and 155 grams
Between 155 and 165 grams
Over 165 grams

Astudent is determining the influence of different types of food on the growth rate of spiders. she feeds one group of spiders two caterpillars twice a week. the other group received similarly-sized beetles twice a week. she records the amount of time required for individuals to reach sexual maturity. her hypothesis is that the spiders feeding on caterpillars will have a faster growth rate because caterpillars have a higher protein content compared to beetles. in this experiment, what is the dependent variable? spiders assigned to different feeding groups. time required to reach sexual maturity number of prey items fed twice a week. growth rates of each group.