Radium undergoes alpha decay and forms A. A undergoes alpha decay and forms B. Which of the following corresponds to A and B? A- Rn 222
A- Th 232
B- U 238
B- Po 218

Expresa commuter train leaves downtown sation and travels at a average speed of 55 miles per hour towards the north side sation, which is 50miles away. thirty minutes later, express commuter train #7 leaves north side and travels at a average speed of 35miles per hour towards downtown sation. at the moment the two trains pass each other, how far(in miles) is train #12 from the downtown sation and how long(in minutes) has the #12 train been traveling