The mean length of 7 planks of wood is 1.35m. When an extra plank of wood is added, the mean length of a plank of wood increase to 1.4m. the length of the extra plank of wood that was added is Select one a. 2. 4 b. 1 C. 1.25 d. 1.75V​

Hello There!

Mean = Sum of observation / total number of observation

Mean = 1.35m

1.35  = Sum of length of 7 wood planks/ 7

1.35*7 = Sum of the length of 7 wood planks

9.45 = Sum of the length of 7 wood planks

Let the length of extra added wood plank = x

So,

(Sum of the length of 7 wood planks + x) / 8 = 1.4m

(9.45 + x) / 8 = 1.4

9.45 + x = 1.4 * 8

9.45 + x = 11.2

x = 11.2- 9.45

= 1.75

So,

The length of extra added wood plank = 1.75m

Step-by-step explanation:

Mark me brainest please. Hope this helps. Anna ♥

how is that middle school

step-by-step explanation:

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