SPEEDS TIMES DISTANCE GOING TO r 200/r 200 RETURN r-10 200/(r-10) 200 DIFF. 1
The number of 200 has two divisors, 40 and 50, that differ by 10 units and such that if you divide 200 by 40 one time and divide 200 by 50 next time, you will get two quotients, 5 and 4, that differ exactly one units. By making this mental thought experiment, you quickly will get the answer to your question, without using any equations and much faster. ANSWER. The faster rate is 50 miles per hour.