Question 279596
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Pablo can drive 5 times as fast as Oscar can ride his bicycle. If it takes Oscar 4 hours longer than
Pablo to travel 90 miles, how fast can Oscar ride his bicycle?
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Let Oscar's riding-speed be S
Since Pablo's driving-speed is 5 times as fast as Oscar's riding-speed, then Pablo's driving-speed is 5S
With distance being 90 miles, Oscar's time to cover this distance = {{{90/S}}}, while Pablo's is {{{90/(5S) = 18/S}}} 
It's stated that "it takes Oscar 4 hours longer than Pablo to travel 90 miles....". This gives us the
following TIME equation: {{{90/S - 18/S = 4}}}
                                          {{{(90 - 18)/S = 4}}} 
                                                    {{{72/S = 4}}} 
                                                    4S = 72 -- Cross-multiplying
            Oscar's riding-speed, or {{{S = 72/4 = highlight(matrix(1,2, 18, mph))}}}</font></font></font></b></pre>