The number \( 4.0 \times 10^{-5} \) is already written in scientific notation. To express it in standard decimal form, you can move the decimal point 5 places to the left (since the exponent is -5).
Starting with \( 4.0 \):
- Move the decimal point to the left 5 places:
- First, it goes to the left of 4: 0.4
- Then add four zeros: 0.00004
So, \( 4.0 \times 10^{-5} \) in standard decimal form is \( 0.00004 \).