There are 5 black balls and 4 white balls in a bag. One ball is drawn from the bag,

 A. He changed the sign of the coefficient. A negative exponent does not affect the sign of a coefficient in scientific notation. The sign of the exponent determines the direction the decimal is moved in.

B. He rewrote incorrectly; . The exponent is increased to account for the extra place the decimal is moved.

Step-by-step explanation:

Given expression :

[Taking coefficients and exponents separate]

[By law of exponent]

Here he changed the sign of the coefficient. A negative exponent does not affect the sign of a coefficient in scientific notation. The sign of the exponent determines the direction the decimal is moved in.

Convert in scientific form.

In the given explanation he rewrote incorrectly; . The exponent is increased to account for the extra place the decimal is moved.

Thus, option A and B express the errors done by Stephen.