1. Move the decimal point to the left until you have a number between 1 and 10. In this case, we move the decimal one place to the left, giving us 2.58.

2. Count the number of places you moved the decimal. We moved it one place.

3. Multiply the number by 10 raised to the power of the number of places you moved the decimal. Since we moved it one place to the left, the exponent is positive 1.

Therefore, 25.8 in scientific notation is 2.58 x 10¹.