Aptitude and Tech interview questions (Sunday 05)

Q1. A train traveling at a speed of 60 km/hr takes 30 seconds to cross a bridge that is 400 meters long. What is the length of the train?
Q2. If it takes 6 workers 8 days to build a wall, how many days would it take for 9 workers to build the same wall?
Q3. If the ratio of the circumference of two circles is 3:4, what is the ratio of their areas?
Q4. Explain how generators work in Python and give an example of how you would use them to iterate over a large dataset efficiently.
Q5. How do you optimize the performance of MySQL queries and what tools or techniques do you use?

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  1. Let’s first convert the train’s speed to meters per second: 60 km/hr = (60*1000)/3600 = 16.67 m/s. The time taken to cross the bridge is 30 seconds. Therefore, distance traveled by train during this time is 400 meters + length of the train. We can write the equation as 16.67 * 30 = 400 + length of train. Solving for length of the train, we get length of train = 150 meters.

  2. The number of workers and the time they take to complete a task are inversely proportional. We can use the formula: (number of workers) * (time taken) = constant. Let’s call this constant K. So we have, 6 * 8 = K. Therefore, K = 48. To find the time taken by 9 workers, we can write: 9 * T = K, where T is the time taken. Solving for T, we get T = 48/9 = 5.33 days (rounded off to 2 decimal places).

  3. Let the circumference of the first circle be 3x and that of the second circle be 4x. The radius of the first circle will be 3x/(2pi) and that of the second circle will be 4x/(2pi). Therefore, the area of the first circle will be (3x/(2pi))^2pi = (9/4)x^2pi and that of the second circle will be (4x/(2pi))^2pi = 4x^2pi. Therefore, the ratio of their areas will be (9/4)x^2pi : 4x^2pi, which simplifies to 9:16.

  4. In Python, a generator is a type of iterator that allows you to iterate over a large dataset efficiently without having to load the entire dataset into memory at once. A generator produces a sequence of values on-the-fly, as you iterate over it, using the yield keyword instead of the return keyword.

To create a generator in Python, you can define a function that uses the yield keyword instead of return to produce a sequence of values. When the function is called, it returns a generator object that you can iterate over using a for loop or the next() function.
def read_large_file(file_path):
with open(file_path) as f:
for line in f:
yield line

for line in read_large_file(‘large_file.txt’):

  1. To optimize the performance of MySQL queries, some tools and techniques that can be used include:
  • Indexing: Creating indexes on the columns that are frequently used in queries can speed up data retrieval.
  • Query optimization: Rewriting queries to use more efficient algorithms or optimizing the structure of the queries can improve performance.
  • Caching: Caching the results of frequently used queries can reduce the amount of time spent retrieving data from the database.
  • Load balancing: Distributing the workload across multiple servers can help to handle high traffic loads and improve performance.
  • Profiling: Using profiling tools to identify performance bottlenecks and optimize queries accordingly.