Find the common factors of the given term.
10 pq, 20qr, 30rp
∵ 10pq = 2 × 5 × p × q = (2 × 5) × p × q
20qr = 2 × 2 × 5 × q × r = (2 × 5) × 2 × q × r
30rp = 2 × 3 × 5 × r × p = (2 × 5) × 3 × r × p
∴ the common factor = 2 × 5 = 10