A bag has 7 white, 12 green and 9 blue marbles. One marble is drawn at random. Find the probability that the marble drawn from the bag is not white.

Answer

To find the probability that the marble drawn from the bag is not white, we can follow these steps:

### Step 1: Calculate the total number of marbles in the bag.
- The bag contains:
- 7 white marbles
- 12 green marbles
- 9 blue marbles

**Total number of marbles = Number of white marbles + Number of green marbles + Number of blue marbles**

\[ \text{Total} = 7 + 12 + 9 = 28 \]

### Step 2: Calculate the number of marbles that are not white.
- The marbles that are not white include:
- 12 green marbles
- 9 blue marbles

**Total number of non-white marbles = Number of green marbles + Number of blue marbles**

\[ \text{Non-white} = 12 + 9 = 21 \]

### Step 3: Calculate the probability of drawing a marble that is not white.
- The probability \( P \) of an event is given by the formula:

\[ P(\text{not white}) = \frac{\text{Number of non-white marbles}}{\text{Total number of marbles}} \]

Substituting the values we found:

\[ P(\text{not white}) = \frac{21}{28} \]

### Step 4: Simplify the fraction.
- To simplify \( \frac{21}{28} \), we can divide both the numerator and the denominator by their greatest common divisor (GCD), which is 7:

\[ P(\text{not white}) = \frac{21 \div 7}{28 \div 7} = \frac{3}{4} \]

### Final Answer:
The probability that the marble drawn from the bag is not white is \( \frac{3}{4} \).

---