Brain Teasers & Mental Math
Probability / EV: a coin is biased so P(heads) = 0.6. You win $10 on heads and lose $5 on tails. What is the expected value per flip?
Model answer
+$4 per flip.
EV = (0.6)(+$10) + (0.4)(−$5) = $6 − $2 = +$4.
Method: multiply each outcome's payoff by its probability and…
The full, human-reviewed answer is in the bank.
Sign up free and Daily 10 serves you 10 questions a day from all 2,300+ — or go Pro for unlimited reps.
Pro unlocks every model answer — $19.99/mo.
More from Brain Teasers & Mental Math
- You roll one fair six-sided die. What is the probability you roll a number greater than 4?
- Flip a fair coin twice. What is the probability of getting at least one head?
- Draw one card from a standard 52-card deck. What is the probability it is a face card (J, Q, or K)?
- Draw one card from a 52-card deck. What is the probability it is a heart OR a king?
- Roll two fair dice. What is the probability the two dice show the same number (a double)?
- A test for a disease is 99% accurate (99% sensitivity and 99% specificity). The disease affects 1 in 10,000 people. You test positive. What is the probability you actually have it?
Try the real thing
1 / 3M&A & Merger Models
What makes an acquisition accretive or dilutive to EPS?
Superday coming up? Take the cheat sheet.
The technicals and stories to have cold before you walk in — free, one email, no mailing list.
Free tier: 20 cards + 10 daily reps + ALL drills — no credit card required.