Use dimensional analysis to convert 840 mL to L

 " 0.85 L " ; or, write as:  " L " .

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Step-by-step explanation:

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Note the exact conversion:  1000 mL = 1 L  .

840 mL *  =  ? L  ;

The unit of "mL" cancel out; since "mL/mL" = 1 ;

since any non-zero value, divided by itself, results in "1 " ;

 and we have:

   (840/ 1000) L ;

Cancel out a  "zero" for both the number and the denominator:

to get:

  (84/ 100) L ;  

   84 ÷ 100 = 0.84 ;

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The answer is:  0.84 mL ;

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84/100 = ? ; divide each side by "4" ;

 (84÷4)/(100÷4) = 21/25 ;

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The answer is:  0.85 L ; or, write as:  " L " .

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Hope this is helpful to you.  Best of luck!

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19.

step-by-step explanation:

you add the 9 in the tens column since it is a single digit and 9 plus zero is 9 so it is 19

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