Here are a few tips for you:
1- You shouldn't go into calculations before putting in place your structure.
For example, if you're about to calculate the profits, split it into revenues and costs. Understand where the revenue is coming from (e.g., number of rides and price per ride) and what the costs are (e.g., fuel, tolls, registration etc.,) before going into the math.
- Always use visuals for your structure (e.g., in the example above, you can use a tree breaking down the “P" into “R” - “C” and the R/C into the various components.
2- Once you have the structure in place, source the datapoints/inputs (ask questions to ensure you get all the inputs you need before running the math
3- When you get to the actual math, check with the interviewer if he/she requires exact figures or not, then take some time to run the numbers (30sec to 1min).
- Any detailed calculation should be done separately (not on the main structure) with the structure kept only for final clean figures.
- Do not use figures with more than ~4 digits (use K, M and B) to keep your numbers short and clean (e.g., 5,000,000 x 7,000 = 5Mx7K=35B
4- Present your findings top-down, starting with the answer (the profits are equal to x) and then summarizing your approach/inputs.
Best of luck,