Prerequisites - P.2 - Exponents and Radicals - Exercises - Page 24: 32

$-1.25 \times 10^{-4}$

Move the position of the decimal point to the new position between 1 and 2. The power of 10 is equal to the number of digits between the old and new decimal positions. In scientific notation a number is expressed as a number between 1 and 10 multiplied by a power of 10.