Question

A dime is 1.25 mm thick. How many meters high would a stack of dimes worth $50 be?

Answer 1

1.25mm x 50 = 62.5 mm  Now lets change mm to meters.   There are 1000 millimeters in a meter and we are only talking about 62.5 so we are not even at a single meter.  Answers B and C can be eliminated.
 
   meter    decimeter   centimeter    millimeter  (each one is ten times more or less than the previous one depending on where you start.
Since we are changing mm to m, we will get fewer.  Why - try grouping any small things  like 14 days - you get 2 weeks.   72 hours - you get 3 days.  Notice that the number gets lower.  14---->2   and 72------->3
So we can expect our number to get smaller.  The beauty of the metric system it that is based on 10 so it involves moving decimals and adding or subtracting zeros if needed.
 meter    dm     cm   mm
                               62.5
notice that it would take 3 "jumps" to the left to get it under the word meter.   That means our decimal has to move 3 jumps to the left too.  In order to do that we need to add a zero in front of the 6 in 62.5
Correct answer is 0.0625  which is none of the answers above - Notice that the decimal is 3 places left from where it was before (62.5).