Dimensional analysis worksheet
convert 3.42 g into kilograms

1 kilogram  =  1,000 grams

The fraction  (1 kilogram / 1,000 grams) is equal to ' 1 ',
because the numerator and denominator are equal.

So you could multiply your 3.42 grams by that fraction without
changing the value of the 3.42 grams.

                   (3.42 grams)  x (1 kilogram / 1,000 grams)

               =  (3.42 x 1 / 1,000) x (grams - kilogram / grams)

You can cancel 'grams' out of the numerator and denominator of the unit,
and then you have

                     (3.42 x 1 / 1,000)  kilogram

                 =      0.00342 kilogram .

 

The fuzzy edges of shadows are a result of  diffraction