What is 0.25 in scientific notation ?

The scientific notation of 0.25 is 2.5 x 10⁻¹

Scientific notation is used to handle numbers that are very big or very small.

It has 3 parts, the coefficient, the base and the exponent.

There must be 1 digit before the decimal point in the coefficient. 
10 is always the base
the exponent signifies the number of places the decimal has moved from its original location to the location before 1 digit. Positive exponent signifies that the decimal point is shifted to the right. Negative exponent signifies that the decimal point is shifted to the left.

In the above scientific notationl

2. 5 is the coefficient
10 is the base
-1 is the exponent. the decimal point shifted one place to the left.

The answer is 41.7 because 1.39 times 30 is 41.7