SarkariPYQ

SSC Selection Post 2020 PYQ — Question 61

SSC Selection Post - Matriculation Level - 9 Nov 2020 - Shift 3 • Quantitative Aptitude • Q61

Back to paper

The lengths of trains A and B are in the ratio of 2 : 3. They pass a static pole in 4 seconds and 5 seconds, respectively. In what time (in seconds) will they cross each other when they move in the same direction?
 

Show answer & explanation

Correct answer: C

Explanation

The correct answer is option 3 i.e. 50.

Length of Train A = 2x

Length of Train B = 3x

Speed = Length / Time

Speed of A = 2x4=x2\frac{2x}{4} = \frac{x}{2}

Speed of B =  3x5\frac{3x}{5}

Relative speed  = ∣x2−3x5∣=∣5x−6x10∣=x10 \left| \frac{x}{2} - \frac{3x}{5} \right| = \left| \frac{5x - 6x}{10} \right| = \frac{x}{10}

 Total length  = 2x + 3x = 5x

Time  = Distance / Relative speed  =  5xx10=5x⋅10x=50\frac{5x}{\frac{x}{10}} = 5x \cdot \frac{10}{x} = 50   seconds