Let's start by imagining a rock being thrown to the air. Let's say that going up is the positive direction and so, going down is the negative. The acceleration is pointing down (because of gravity) so it's always negative. While the rock is going up, it's velocity/speed is positive, but the acceleration is negative. While the rock is going down, both acceleration and speed are negative. This shows that the first statemente is true, but the second is false. You can also think that if you define going DOWN as the POSITIVE direction, you can have both positive acceleration and speed, or positive acceleration and negative speed.
You would multiply the students by the price (12*10=120) then multiply chaperones by price (6*15=90) then add both prices together to get 210. Then you would subtract 210 from 380 to get how many boys are in the class. 380-210=170. Since each student cost 10 so you would divide 170/10=17. There would be 17 boys in your class.
