CAT 2015 Quantitative Ability

Let the four numbers be XK, XL. XM and XN.
where X is the common factor of each pair possible pair of numbers and K, L, M, N are prime to each other
310 = 2 × 5 × 31
651 = 31 × 21 = 3 × 7 × 31
∴ GCF (310, 651) = 31
which is the highest common factor of all.