A bacteria culture starts with 1 cell and doubles every hour, so after 100 hours it has $2^{100}$ cells. One cell is then removed for testing. What is the unit digit of the number of cells left, $2^{100} - 1$ ?

1Correct answerYour answer3Correct answerYour answer5Correct answerYour answer7Correct answerYour answer

Show the answer and explanation

CorrectNot quiteAnswer C

Correct answer: C

Worth noting

A remainder of 0 means the LAST digit of the cycle (6), not the first (2); using 2 gives 1.

Ten questions from Number System, at your own pace.

A bacteria culture starts with 1 cell and doubles every hour, so after 100 hours it has 21002^{100}2100 cells. One cell is then removed for testing. What is the unit digit of the number of cells left, 2100−12^{100} - 12100−1?