A. 1.9 is an irrational number
18$-8$book=20pencils that were 10$.
and Brian had 80 cards work: 80÷2= 40+10 new cards=50 cards
Swapping rows alters the sign of the determinant:

Multiplying a single row by a scalar scales the determinant by the same amount:

Then

The better buy would be the 36 bottles of water for 4$ because it would be 9 bottles per dollar other than the 24 which is 8 bottles per every dollar. Hope it helps!
The sum of their speeds is 380 miles per hour. The difference of their speeds is 30 miles per hour. Then the faster plane is traveling at
.. (380 +30)/2 = 205 miles per hour
The slower plane's speed is 30 miles per hour less, so it is traveling at
.. 205 mph -30 mph = 175 miles per hour