Complete the steps to evaluate the subtraction expression (below)

Question

(2.1x10⁹)-(9.7x10⁹)=(________x10⁷)-(9.7x10⁷)

                             =(________-________)x10⁷

                             =_________x10⁷

                             =_________x10⁹

Answer 1

When we increase the exponents, we move the decimal point the same number of places from its current position as the increase to the left.

 

When we decrease the exponents, we move the decimal point the same number of places from its current position as the decrease to the right.

 

 

(2.1 × 10⁹) - (9.7 × 10⁹) = (210 × 10⁷) - (970 × 10⁷)

 

 

In the second row, we use distributive property.  Notice that 10⁷ is the common factor.  So we have

 

                                     = (210 - 970) × 10⁷

 

 

In the third row, we just simplify the term that is in parenthesis.

 

                                     = -760 × 10⁷

 

                                     = -7.60 × 10⁹