Passage: In 1946, the Viet Minh  government (later to become the government of North Vietnam) introduced its own currency, the đồng, to replace the French Indochinese piastre at par. Two revaluations followed, in 1951 and 1959; the first was at a rate of 100:1, the second at a rate of 1,000:1.

Question: What years did the revaluations come about?
1951 and 1959