What is 1,050 decreased by 20% ??

How to determine whether two known pairs of points are on the same line.

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

Which of the following pair(s) of circles have las a common external tangent? select all that apply. a and b a and c b and c