Write 0.416666667 correct to 3 significant figures. Express 12000 in Standard form.

The first non-zero digit is 4, so it is the first significant figure.
The second significant figure is 1.
The third significant figure is 6.
So, we are looking at 0.416.

The digit after the third significant figure (6) is 6.

Since the digit 6 (the fourth significant figure) is 5 or greater, we round up the third significant figure (6) by adding 1 to it.
$6 + 1 = 7$.

The number becomes 0.417.
The number 0.416666667 correct to 3 significant figures is $\boxed{\mathbf{0.417}}$.

9. Express 12000 in Standard form.

The number 12000 has an implied decimal point at the end (12000.).
To get a number between 1 and 10, we move the decimal point to after the first digit, 1. This gives us 1.2.

The decimal point was moved 4 places to the left (from 12000. to 1.2).

Since the decimal point was moved 4 places to the left, the exponent of 10 is positive 4.

The number 12000 in standard form is $\boxed{\mathbf{1.2 \times 10^4}}$.

10. Write $2.36 \times 10^{-3}$ as a decimal number (ordinary form).

The exponent is $-3$.

A negative exponent means we move the decimal point to the left. The number of places to move is the absolute value of the exponent, which is 3.
Starting with 2.36, move the decimal point 3 places to the left.

The decimal number (ordinary form) is $\boxed{\mathbf{0.00236}}$.