LinkedIn·Data Scientist·Technical Phone Screen
Jul 2026
LinkedIn data scientist interview that went deep into probability theory, specifically around coin flip stopping times. Not your typical SQL or metrics question, this one felt more like a grad school exam than a product interview.
- For a fair coin, what is the expected number of flips until you see two consecutive heads? Derive it using a state-based or Markov chain argument.
- Now generalize: if the coin has probability p of heads, what is the expected number of flips to see HH?
- For the fair coin case, derive the variance of T, the number of flips until HH appears. Walk through your full reasoning.
“I set up three states: start, one head seen, done.” The rest of the author's notes on Data Scientist interview at LinkedIn, Technical Phone Screen round, covers how they worked through the question, what the panel pushed back on, and what they would do differently.
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