Tell how to find 81-16 using mental math

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

Define multiplicative inverse. give an example of a number and its multiplicative inverse.

Choose the more precise measurement. 26.4 cm or 8.39 cm