Muhammad's pennies
Discrete Mathematics
Level
2
Jenny places \( 100 \) pennies on a table, with \( 30 \) showing heads and \( 70 \) showing tails. She chooses \( 40 \) distinct pennies uniformly at random and turns them over. That is, if a chosen penny was showing heads, she turns it to show tails; if a chosen penny was showing tails, she turns it to show heads. After this process, what is the expected number of pennies showing heads?
This problem is shared by Muhammad A.
by
Calvin Lin