What should come in place of the question mark '?' in the following number series?

510, ?, 210, 160, 135, 122.5

- 315
- 310
- 290
- 350
- None of these

Option 2 : 310

**Calculation:**

The series follows following pattern:

⇒ 510 – 200 = **310**

⇒ 310 – 100 = 210

⇒ 210 – 50 = 160

⇒ 160 – 25 = 135

⇒ 135 – 12.5 = 122.5

**∴ The value of ? is 310**

**Note: **Difference is divided by 2

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