Differences between looping and simersaulting​

When you turn on a battery-operated device, an electrical circuit is

In which item is energy stored in the form of gravitational potential energy? a. a slice of bread b. a compressed spring c. an apple on a tree d. a stretched bow string

The radioactive isotope of lead, pb-209, decays at a rate proportional to the amount present at time t and has a half-life of 3.3 hours. if 1 gram of this isotope is present initially, how long will it take for 80% of the lead to decay? (round your answer to two decimal places.)