Train X travels from City A to City B, a distance of 630 miles, in t

Question

Train X travels from City A to City B, a distance of 630 miles, in t hours.

Train Y completes the same trip in (t – 3) hours.

Select possible average speeds for train X and train Y, respectively, in miles per hour (mph). The answers must be jointly consistent with the problem. Make only one selection in each column.

chetan2u · Accepted Answer

Train X a takes three more hour, so divide 630 by all the options given and where ever the difference is 3, the higher speed is of Y and lesser is that of X.
 \frac{630}{15}=\frac{2*3*3*5*7}{3*5}=42 
 \frac{630}{18}=\frac{2*3*3*5*7}{2*3*3}=35 
 \frac{630}{21}=\frac{2*3*3*5*7}{3*7}=30 
 \frac{630}{30}=\frac{2*3*3*5*7}{2*3*5}=21 
 \frac{630}{35}=\frac{2*3*3*5*7}{5*7}=18

21-18=3, so speed of X is 30, while that of Y is 35.
    Train X    Train Y    Speed in mph   
      15  
      18  
      21  
  X    30  
    Y  35  
      45

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Train X travels from City A to City B, a distance of 630 miles, in t

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Train X travels from City A to City B, a distance of 630 miles, in t

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