Statistics problem of the day
Today's problem
Something happens 65 per cent of the time. In 9 independent tries, what is the chance of exactly 4 of them working out? Answer as a percentage.
Type your answer with two decimals. Within one per cent counts as close, and the arrow points from your answer to the right one.
Yesterday's answer23.81
How does the statistics problem of the day work?
Everyone gets the same problem today, and it changes at midnight UTC. Read the statement, do the maths, and type what you got. You have eight tries, and each one says whether the right answer is higher or lower than yours.
The answer is not in the page. Only the statement is, because you need it to solve the problem.
Which standard deviation is asked for?
The sample one, with n minus 1 in the divisor. Dividing by n gives the population standard deviation, which answers a different question and is the most common slip in the first weeks of any course. The statement always says which one it wants.
What exactly does the binomial question ask?
The chance of exactly that many successes, not of that many or more. It is the number of ways to choose which tries succeed, times the chance of a success to that power, times the chance of a failure to the power of the rest.
How close does my answer have to be?
Within one per cent of the right value counts as close, and the exact value to the second decimal counts as exact. One per cent of the answer itself, not a fixed amount.
Can I use a calculator?
Yes. This is a problem to solve, not a memory test. The site has calculators for descriptive statistics, and using them is the point of having them.