There is no definitive answer for several reasons:
It is calculated that at the time of the Norman conquest in 1066 there were around 1000 monks and nuns in about 60 Saxon monastic houses in England. These were almost entirely destroyed and rebuilt in the Norman style, with additional monasteries founded by wealthy Normans; by 1100 there were possibly 70 monasteries for monks and 12 for nuns in England and Wales.
By 1175 an astonishing 155 more monasteries had been built - this was the peak of monasticism in England.
Each monastery housed varying numbers of monks: some had as few as 20 or 30, others up to 200. Numbers dropped very sharply in the early 1500s when it became clear that king Henry VIII intended to take over the Church's wealth, lands and property.
If you take an average of 70 monks per monastery and multiply it by 250 monasteries (a very approximate figure for the end of the 12th century) you arrive at roughly 17,500 monks; figures for nuns are even more difficult to guess but there were perhaps between two and three thousand, perhaps more.
Some examples of fluctuating numbers: in the mid-12th century at Rievaulx Abbey (Yorkshire) there were 140 monks and 500 lay brothers; by 1538 there were just 23. In 1125 at Abingdon there were 80 monks, but just 25 in 1538.
Monks
They lived in monasteries
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Not all monks taught in schools during the Middle Ages as not all monasteries had schools. However, many communities did operate what would be called schools today.
During the Middle Ages the monks were the people who preserved books and wrote books. The population of the Middle Ages couldn't read or write and there were really no schools for them to go to. Monks spent years creating and copying books. One of the great books that was done in this time was the Book of Kells.
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it actually helped the monks achieve zen
work
by monks in middle ages
There were lots and lots of monks in the Middle Ages. Nuns, too. Roger Bacon was a famous monk of the period, and Hildegard of Bingen was a famous nun.
In an nunnery. Monks lived in Monerstrys.
Monks took vows of poverty, chastity, and obedience. There is a link below to the section on early Christianity of an article on Christian monasticism.