Why is the sum of a rational number and its opposite always equal to 0

8) A submarine left Hawaii two hours before an aircraft carrier. The vessels traveled in opposite directions. The aircraft carrier traveled at 25 mph for nine hours. After this time the vessels were 280 mi. apart. Find the submarine's speed.

An item is regularly priced at $90. Manuel bought it at a discount of 70% off the regular price. How much did Manuel pay? m

In a school that has 20 teachers, 10 teach Mathematics, 8 teach Social Studies, and 6 teach Science. Two teach both Mathematics and Social Studies, but none teach both Social Studies and Science. How many teach both Mathematics and Science?

What is the closest benchmark for 52%

A florist received a shipment of 16 dozen roses the original order was for 20 dozen what percentage of the order did not arrive?

The length of a rectangle is three times the width. What is the perimeter of the rectangle if the width is 17 inches? 136 inches 204 inches 51 inches 68 inches

The length of a garden is 25 feet. What must the width of the garden be, in a whole number of feet, so the area is greater than 200 square feet but less than 300 square feet?

Solve for x - 2x + 5<7 a) x>-1 b) xc-1 c) x>-6 d) x<-6

Expand and simplify (7+6y) ^2

A bag contains 6 blue marbles, 10 red marbles, and 9 green marbles if two marbles are drawn at random without replacement what is the probability that two green marbles are drawn