A boat leaves a dock at 5:00 PM and travels due south at a speed of 20 km/h. Another boat has been heading due east at 15 km/h and reaches the same dock at 6:00 PM. How many minutes after 5:00 PM were the two boats closest together

After 21.6 minutes after 5:00 pm boats are closest to each other.

Step-by-step explanation:

Speed of the first boat = 20

Let after time t the distance between the boats is minimum.

Distance traveled by the first boat in time t is = 20 t ------- (1)

Speed of the second boat = 15

Distance traveled by the second boat in time t is = 15 t ------- (2)

From the diagram

Distance AB = 15 - 15 t --------- (3)

Distance between the boats is at time t is AC. And it is calculated by

Differentiate above equation with respect to t we get,

2 (15 - 15 t) (-15) + 2 (20 t) (20)

- 450 + 1250 t

for the distance to be minimum 0

⇒ - 450 + 1250 t = 0

⇒ t =

⇒ t = 0.36 hours

⇒ t = 21.6 minutes

Therefore the distance between the boats after 21.6 minutes after 5:00 pm is minimum.

5x+40

5(x + 8)

7x - 49

7(x - 7)

18x + 9

9(2x + 1)

15x - 10

5(3x - 2)

step-by-step explanation:

for number one all you have to do is factor 5 out of 5x + 40

for number 2 factor 7 out of 7x - 49

for number three factor 9 out of 18x + 9

for number four factor 5 out of 15x - 10

the 3rd on is correct

step-by-step explanation: