When you move the decimal point to the right, you decrease the value of the exponent in the power of 10.
When you move the decimal point to the left, you increase the value of the exponent in the power of 10.

(1)    1200 = 1.2 x 103

The original decimal value is divided by 1000, so the coefficient  of 1.2 has to be multiplied by 1000, or 103.
The decimal point is moved three places to the left and the exponent is increased by three.

(2)    439 = 4.39 x 102

The original decimal value is divided by 100, so the coefficient  of 4.39 has to be multiplied by 100, or 102.
The decimal point is moved two places to the left and the exponent is increased by two.

(3)    1635.8 = 1.6358 x 103

The original decimal value is divided by 1000, so the coefficient  of 1.6358 has to be multiplied by 1000, or 103.
The decimal point is moved three places to the left and the exponent is increased by three.

(4)    0.025 = 2.5 x 102

The original decimal value is multiplied by 100, so the coefficient  of 2.5 has to be divided by 100, or 102.
The decimal point is moved two places to the right and the exponent is decreased by two.

(5)    0.000168 = 1.68 x 104

The original decimal value is multiplied by 10,000, so the coefficient  of 1.68 has to be divided by 10,000, or 104.
The decimal point is moved four places to the right and the exponent is decreased by four.

(6)    1200 x 106 = 1.2 x 109

The decimal point is moved three places to the left and the exponent is increased by three.

6)    0.934 x 1012 = 9.34 x 1011

The decimal point is moved one places to the right and the exponent is decreased by one.

(7)    0.002 x 109 = 2.0 x 106

The decimal point is moved three places to the right and the exponent is decreased by three.

(8)    1899405 x 10-4 = 1.89945 x 102

The decimal point is moved six places to the left and the exponent is increased by six.

 

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