Question 574575
The way to approach these is to think in terms
of the units only. Work it out as units, and then
plug in the numbers.
Working step-by-step:
( strides / cm ) x ( cm/m )
Rewrite this as:
( cm/cm ) x ( strides/m )
Now you want:
( cm/cm ) x ( strides/m ) x ( m/km )
Now rewrite this as:
( cm/cm ) x ( m/m ) x ( strides/ km )
This is the right approach as far as units go
Everything cancels except ( strides / km )
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Now work backwards toward actual unit conversions:
( strides/cm ) x ( cm/m ) x ( m/km ) = ( strides/km )
This is exactly the same as:
( cm/cm ) x ( m/m ) x ( strides/ km )
with multipliers and divisors just shifted around
Now, and only now, plug in numbers.
multiply by {{{ 16 }}} km, and you end up with
a single unit: ( strides ), which is what you want
( strides/cm ) x ( cm/m ) x ( m/km ) x ( km ) = ( strides )
{{{ ( 1/80 )*( 100/1 )*( 1000/1 )*( 16 )  = 20000 }}}
Wally needs 20,000 strides to cover 16 km
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I never, but never, jump right into the numbers. I learned the
units method in high school physics where the teacher would
fill a blackboard with just unit conversions.