how many significant figures are in this number ? 0.40001

Explanation:

Step1: Recall significant figure rules

Leading zeros (before the first non - zero digit) are not significant. Non - zero digits are significant. Zeros between non - zero digits are significant. For the number (0.40001), the leading zero (the one before 4) is not significant. The digit 4 is non - zero and significant. The zeros between 4 and 1 are between non - zero digits, so they are significant. The digit 1 is non - zero and significant.

Step2: Count the significant figures

Let's list the significant digits: 4, 0, 0, 0, 1. Counting these, we have 5 significant figures.

Answer:

5