Aparticle is moving along the curve y= 5sqrt(5x+4) . as the particle passes through the point (1,15), its x-coordinate increases at a rate of 4 units per second. find the rate of change of the distance from the particle to the origin at this instant.

Aclassroom is made up of 11 boys and 14 girls. the teacher has four main classroom responsibilities that she wants to hand out to four different students (one for each of the four students). if the teacher chooses 4 of the students at random, then what is the probability that the four students chosen to complete the responsibilities will be all boys?