You should use && instead of || : if ( speed<=74 && speed >55 )
You can make your code shorter using something like this:
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if (speed >= 75)
cout<< "Your Too Fast";
elseif( speed > 55 )
cout<< "Not Bad Your not too Fast";
elseif( speed >= 45)
cout<< "Medium";
else
cout<< "Your Too Slow";