Unlimited drills
Every drill writes a brand-new question each time — new numbers, new code — so you can practise a skill as long as you like. Correct answers earn 2 points, up to 60 a day.
Coding & data structures
JavaScript: filter and reduce
What does a filter → reduce chain return?
JavaScript: Array.slice
Which elements does slice(start, end) return?
JavaScript: + with strings
Predict string concatenation vs addition.
Python: list slicing with a step
Predict lst[start:stop:step].
Binary search comparisons
Worst-case comparisons on a sorted array.
Time complexity of a loop
Read the loops, name the Big-O.
Bitwise AND, OR, XOR
Work a bitwise operation on two bytes.
Decimal to binary
Convert a number to base 2.
SQL: COUNT and SUM with WHERE
Run an aggregate query in your head.
Finance & accounting
Simple interest
Interest on a principal at a flat yearly rate.
Compound interest
Maturity value with yearly compounding.
Loan EMI
Monthly instalment on a reducing-balance loan.
GST on an intra-state sale
CGST and SGST on a taxable value.
Price before GST
Back out the taxable value from a GST-inclusive price.
Straight-line depreciation
Yearly charge with a salvage value.
Written-down value
Book value after reducing-balance depreciation.
Break-even units
Units needed to cover fixed costs.
Gross margin
Gross profit as a share of revenue.
Current ratio
Liquidity from current assets and liabilities.
CAGR
Compound annual growth rate between two values.
Net present value
Discount three years of cash flows.
Employee PF contribution
Monthly employee share at a stated rate.
Marketing & sales
Click-through rate
Clicks as a share of impressions.
Return on ad spend
Revenue earned per rupee of ad spend.
Cost per acquisition
Spend divided by conversions.
Conversion rate
Share of visitors who convert.
Customer acquisition cost
All sales and marketing cost per new customer.
Customer lifetime value
Gross-margin LTV from monthly churn.
Monthly churn rate
Customers lost as a share of those at the start.
Weighted pipeline
Deal values times their win probability.