`336,168,84,42,21,?`

Answer

To solve the number series `336, 168, 84, 42, 21, ?`, we can observe the pattern in the sequence. Let's analyze it step by step.

### Step 1: Identify the relationship between the numbers
We can see that each number in the series is half of the previous number.

- \( 336 \div 2 = 168 \)
- \( 168 \div 2 = 84 \)
- \( 84 \div 2 = 42 \)
- \( 42 \div 2 = 21 \)

### Step 2: Continue the pattern
Now, we need to find the next number in the series after 21. Following the same pattern, we divide 21 by 2.

- \( 21 \div 2 = 10.5 \)

### Conclusion
Thus, the next number in the series is **10.5**.