To find the number of different combinations of shoes Rachel can bring, we can use the combination formula.
The number of combinations of selecting 2 pairs of shoes out of 8 pairs is given by the formula:
C(n, r) = \frac{{n!}}{{r!(n-r)!}}
where n is the total number of pairs of shoes and r is the number of pairs she wants to bring.
In this case, n = 8 and r = 2. Plugging in these values into the formula, we get:
C(8, 2) = \frac{{8!}}{{2!(8-2)!}}
Simplifying the expression:
C(8, 2) = \frac{{8!}}{{2!6!}}
C(8, 2) = \frac{{8 \times 7 \times 6!}}{{2! \times 6!}}
Canceling out the common terms:
C(8, 2) = \frac{{8 \times 7}}{{2 \times 1}}
C(8, 2) = \frac{{56}}{{2}}
C(8, 2) = 28
Therefore, Rachel can bring 28 different combinations of shoes on her road trip.