12 thousandth is the same as 0.012, so to put something in scientific notation you move the decimal point to the left or right until it is between the first two numbers. So:
Moving the decimal for 0.012 to between the first two numbers, we get: 1.2
For every move of the decimal place to get there, we divide/multiply by 10 each time. In this case, we multiply by 10 each time.
To get to 1.2, we had to move the decimal 2 times, so the answer is 1.2×10^-2
When you move the decimal to the right, the value of the power is negative, and when you move it to the left it is positive.
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