Bob is hiking down a 12-mile country trail. He could hike at 3 mph for the first two hours and then go the rest of the way at 5 mph or he could just go the whole way at 4 mph. How long would each of these options take? Which option is the faster?
The first option would take:
The second option would take:
The faster option is the:

The first option would take: 3.2 hr

The second option would take: 3 hr

The faster option is the: second

Step-by-step explanation:

Below in bold.

Step-by-step explanation:

Speed = distance / time.

First option:

Walking  at 3mph for 2 hours will give 2*3 = 6 miles.

So for 6 miles travelling at 5 mph he will take 6/5 = 1.2 hours.

Total time = 3.2 hours.

Second option:

Walking for 12 miles at 4 mph will take him 12/4 = 3 hours.

The fastest option is the second one.

the value of v.w= -12.

step-by-step explanation:

we are given three vector r,v and w as:

r = < 5, -5, -2> ; v = < 2, -8, -8> ; w = < -2, 6, -5>

we know that r,v and w could also be represented as:

r=5i-5j-2k

v=2i-8j-8k

and w= -2i+6j-5k

where i,j and k are the unit vectors of x,y and z-axis respectively.

also we know that it has the following property:

i.i=1 ; j.j=1; k.k=1

and i.=j.i=i.k=k.i=j.k=k.j=0

i.e. when we multiply two vectors or we find it's dot product we need to only multiply the components of x coordinates with each other; y with each other and z with each other.

hence, v.w= (2i-8j- -2i+6j-5k)

                  = 2×(-2)+(-8)×(6)+(-8)×(-5)

                  = -4-48+40

                  = -12

hence, v.w= -12