Question 835538
These all use the formula
{{{ d = r*t }}}, or
( distance ) = ( rate )*( time )
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There are 2 other ways to express this formula:
{{{ r = d/t }}}
( rate ) = ( distance ) / ( time )
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{{{ t = d/r }}}
( time ) = ( distance ) / ( rate )
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After 3 hours a car has covered a distance of 90km. 
How fast (speed) was the car traveling?
For this, you need {{{ r = d/t }}}
{{{ r = 90/3 }}} km/hr
{{{ r = 30 }}} km/hr
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A girl swims 50 meters in 25 seconds. what is her speed?
Again, you need to use: {{{ r = d/t }}}
{{{ r = 50/25 }}} m/sec
{{{ r = 2 }}} m/sec
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What is the speed of a car that travels 420km in 6 hours? 
{{{ r = 420/6 }}} km/hr
{{{ r = 70 }}} km/hr
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How fast do you walk if you take 2.5 hours to cover 12.5km?
{{{ r = 12.5/2.5 }}} km/hr
{{{ r = 5 }}} km/hr