Coding Grandmaster · project 24 of 46 · premium, free for now

How computers fake randomness

Write next_value(seed) with that formula, and roll(seed) = 1 + seed % 6. Starting from the given seed, roll 600 times (feeding each result back in) and print how many times each face 1 to 6 came up.

Learn

A computer cannot flip a coin. It runs a formula that scrambles a number into the next one, giving a stream that looks random but is completely determined by the starting seed. A linear congruential generator does it with next = (seed × 1103515245 + 12345) mod 2^31. Use the same seed and you get the same stream, which is exactly what makes simulations repeatable.

Your task

Write next_value(seed) with that formula, and roll(seed) = 1 + seed % 6. Starting from the given seed, roll 600 times (feeding each result back in) and print how many times each face 1 to 6 came up.

Stretch challenge

Estimate pi by dropping random points in a square with this generator.

← The binomial distribution Averages →

Python

Press Run to see what your program prints.

Keep going in Coding Grandmaster

Counting outcomes

Write ways(target), the number of dice pairs that add up to target, and as_fraction(top, bottom) that returns text like 1/6 in lowest terms. Print the chance of a total of 7.

Start →20

The OR rule

Build the 52-card deck as (rank, suit) pairs, then count the cards that are the chosen suit, the chosen rank, both, and either. Print the four counts and the chance of either as a fraction in lowest terms.

Start →21

Given that…

For the chosen club print how many students are in it, how many passed, and P(passed | club) as a percentage with one decimal place. Then print P(passed) for all students.

Start →22

Bayes and the medical test

Write posterior(prior, sensitivity, specificity) returning P(sick | positive) rounded to 4 decimal places. Print it for prior 0.01, sensitivity 0.9, specificity 0.9.

Start →23

The binomial distribution

Write binomial(n, k, p) and use it to print the chance of exactly 3 heads in 5 fair flips, the chance of at least 4 heads, and the total of all the chances (rounded to 6 places).

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FAQ

How computers fake randomness: common questions

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