Computer calculation speeds are usually measured in nanoseconds. A nanosecond is 0.000000001 seconds. Which choice expresses this very small number using a negative power of 10?
А.
10-8
B.
10-9
С
10-10
D
10 11

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