Question 10
Positive integers $a,b,c$ are selected randomly from $\{1,2,\ldots,2020\}$ with replacement. Find the probability that $abc+ab+2a$ is divisible by 5.
Answer entry: use a reduced fraction a/b or a decimal with a dot, without spaces. Only explicitly listed exact forms are recognized; equivalent forms outside that list require manual checking and must not be treated as wrong or scored zero solely for nonrecognition. No symbolic fraction parser is claimed.
Answer entry: use a reduced fraction a/b or a decimal with a dot, without spaces. Only explicitly listed exact forms are recognized; equivalent forms outside that list require manual checking and must not be treated as wrong or scored zero solely for nonrecognition. No symbolic fraction parser is claimed.