Hello I am working on pretest questions, and I am completely lost. Ive read the textbook, however the textbook we use, isnt the greatest. I am stuck ona few questions, any guidance on how to approach these questions and formulas to use would be appreciated 1) 235U decays to 207Pb by a combination of alpha decays and beta- decays. How many beta- and alpha decays are involved in the whole series? The atomic # of U is 92 and the atomic number of Pb is 82. 2) The physical half life of 109Cd is 460d. A new source of activity 1-GBq is purchased. The source can be used until its activity decreases to 2.0 GBq. How long does it take for the source activity to fall from 10GBq to 2.0 GBq? THANKS!!