You have a well-shuffled 52-card deck. on average, how many pairs of adjacent cards are there such that both cards are red?

Pair 1: A & 2
Pair 2: 2 & 3
Pair 3: 3 & 4
Pair 4: 4 & 5
Pair 5: 5 & 6
Pair 6: 6 & 7
Pair 7: 7 & 8
Pair 8: 8 & 9
Pair 9: 9 & 10
Pair 10: 10 & J
Pair 11: J & Q
Pair 12: Q & K
Pair 13: K & A

There are 13 pairs in Diamond & 13 pairs in Heart,

So, Total pairs are 26,

Therefore, 26 is the correct answer.