Explanation

Step 1: Find the differences between consecutive terms

66 → 63 → difference = 66 − 63 = 3

63 → 57 → difference = 63 − 57 = 6

57 → 45 → difference = 57 − 45 = 12

So the differences are: 3, 6, 12, …

Step 2: Observe the pattern in differences

3 × 2 = 6

6 × 2 = 12

Pattern: The difference doubles each time.

Next difference = 12 × 2 = 24

Step 3: Find the next number

Last number = 45

Subtract next difference: 45 − 24 = 21

Explanation

Letters decrease by 2 in alphabetical order: Z → X → V → T → R

Numbers increase by 2: 3 → 5 → 7 → 9 → 11

Explanation

Step 1: Look at the differences alternately

1. 115 → 55 = −60

2. 55 → 170 = +115

3. 170 → 65 = −105

4. 65 → 235 = +170

Step 2: Find the pattern in differences

• Negative differences: −60, −105, … (increasing magnitude)

• Positive differences: +115, +170, … (increasing by 55 each time)

  
  

Step 3: Find the next number

• Last number = 235

• The pattern alternates between negative and positive

• Next difference = −160 (fits pattern of increasing negative difference magnitude: 60, 105, 160)

Explanation

To complete the series, the pattern is increasing the letters by a certain number each time.

The series goes as follows: B (+3) E (+5) J (+7) Q (+9).

Therefore, the next letter should be 9 letters after Q, which is X.

Explanation