align* 3128 &= 313 &= 31!28!3! &= 31 30 293 2 1 &= 31 303 2 1 29 &= 31 5 29 &= 4495. align*

jmc

counting and probability junior

Problem

Compute

(28 31)

Solution

(28 31) = (3 31) = \frac{31 !}{28 ! 3 !} = \frac{31 \times 30 \times 29}{3 \times 2 \times 1} = 31 \times \frac{30}{3 \times 2 \times 1} \times 29 = 31 \times 5 \times 29 = 4495 .

Final answer

4495