A bag contains 2 white marbles, 1 black marble, and 4 gray marbles. What is the probability of drawing each color, and which color is least likely to be drawn?

The least likely color is the one with the fewest marbles.
There is 1 black marble, 2 white marbles, and 4 gray marbles.
The least likely color is black.

1. The color marble least likely to be drawn from the bag is $\boxed{\text{Black}}$.

Probability is calculated as $\frac{\text{Number of favorable outcomes}}{\text{Total number of outcomes}}$.
Number of black marbles = 1
Total marbles = 7

$$P(\text{Black}) = \frac{1}{7}$$

2. The probability of drawing a black marble from the bag is $\boxed{\frac{1}{7}}$.

Number of gray marbles = 4
Total marbles = 7

$$P(\text{Gray}) = \frac{4}{7}$$

3. The probability of drawing a gray marble is $\boxed{\frac{4}{7}}$.

Number of white marbles = 2
Total marbles = 7

$$P(\text{White}) = \frac{2}{7}$$

4. The probability of drawing a white marble is $\boxed{\frac{2}{7}}$.

Number of marbles that are not white = Number of black marbles + Number of gray marbles = $1 + 4 = 5$
Total marbles = 7

$$P(\text{Not White}) = \frac{5}{7}$$

5. The probability of drawing a marble that is not white is $\boxed{\frac{5}{7}}$.

Number of marbles that are not black = Number of white marbles + Number of gray marbles = $2 + 4 = 6$

$$P(\text{Not Black}) = \frac{6}{7}$$

Number of marbles that are not gray = Number of white marbles + Number of black marbles = $2 + 1 = 3$

$$P(\text{Not Gray}) = \frac{3}{7}$$

Since $\frac{6}{7} > \frac{3}{7}$, you would be more likely to draw a marble that is not black. 6. You would be more likely to draw a marble that is not black. This is because there are 6 marbles that are not black (2 white + 4 gray), while there are only 3 marbles that are not gray (2 white + 1 black).

Original black marbles = 1
Added black marbles = 3
New number of black marbles = $1 + 3 = 4$
Original total marbles = 7
Added marbles = 3
New total marbles = $7 + 3 = 10$

$$P(\text{New Black}) = \frac{4}{10} = \frac{2}{5}$$

7. If three more black marbles were added to the bag, the probability of drawing a black marble would be $\boxed{\frac{2}{5}}$.