Foundation · Case math
Case math and quantitative reasoning
The arithmetic cases use, from the ground up: percentages and percentage points, growth, margins, breakeven, payback, return on investment, present value, and the mental-math habits that keep you fast and correct.
21 min3 lessons Last reviewed
Start lesson 1 The arithmetic, from the ground up
Key takeaways
- Percent and percentage points are different: If a margin goes from 10 percent to 12 percent, it rose by 2 percentage points, but by 20 percent (2 is 20 percent of 10).
- Perpetuity shortcut: a cash flow that continues every year with no end is worth the yearly amount divided by the discount rate.
- Always sanity-check. After any answer, ask: is this number possible?
By the end you will be able to
- Do percentages, percentage points, and growth rates cleanly in your head
- Move between profit, margin, markup, and breakeven
- Judge an investment with payback, ROI, net present value, and the perpetuity shortcut
- Handle large numbers, including lakh and crore, without losing a zero
Lessons
1
The arithmetic, from the ground up
Percentages, percentage points, growth over several years, margins, and breakeven.
10 min
2
Judging an investment: payback, ROI, and present value
Payback, return on investment, net present value, and the perpetuity shortcut cases often use.
6 min
3
Fast, clean, and checked
Mental-math habits, large numbers (million, billion, lakh, crore), calculating out loud, and sanity checks.
5 min