Four institutes, A, B, C, and D, had contracts with four vendors W, X, Y, and Z during the ten calendar years from 2010 to 2019. The contracts were either multi-year contracts running for several consecutive years or single-year contracts. No institute had more than one contract with the same vendor. However, in a calendar year, an institute may have had contracts with multiple vendors, and a vendor may have had contracts with multiple institutes. It is known that over the decade, the institutes each got into two contracts with two of these vendors, and each vendor got into two contracts with two of these institutes.
The following facts are also known about these contracts.
I. Vendor Z had at least one contract in every year.
II. Vendor X had one or more contracts in every year up to 2015, but no contract in any year after that.
III. Vendor Y had contracts in 2010 and 2019. Vendor W had contracts only in 2012.
IV. There were five contracts in 2012.
V. There were exactly four multi-year contracts. Institute B had a 7-year contract, D had a 4-year contract, and A and C had one 3-year contract each. The other four contracts were single-year contracts.
VI. Institute C had one or more contracts in 2012 but did not have any contract in 2011.
VII. Institutes B and D each had exactly one contract in 2012. Institute D did not have any contract in 2010.
In how many years during this period was there only one contract?
From IV: A, B, C, D have one 3, 7, 3, 4-year contract respectively and all other contracts are one-year contracts.
I, Z has at least one contract every year, the only possible
combination is 7+3 or 7+4 year contract and that 7-year contract must be
From III, Vendor W had contracts only in 2012 and
from VII, Institutes B and D each had exactly one contract in 2012
=> W has got contracts from A and C.
From II. Vendor X had one or more contracts in every year up to 2015, but no contract in any year after that and from VI, VII: C and D didn't have any contract in 2011 and 2010 respectively => A should have X as a 3-year contract from 2010-2012. Now, for 2013-2015 X can't have B for the same. So, X must have got contracts from either C or D in that period.
X has C as a 3-year contract from 2013-2015 but in this case, D can't have any contract in 2012 so, this case is not valid.
X has D for a 4-year contract from 2012-2015 and C must have Z for a three-year contract in the period 2017-2019 such that Z has at least one contract every year.
It is known that over the decade, the
institutes each got into two contracts with two of these vendors, and
each vendor got into two contracts with two of these institutes => A
hasn't got any contract from 2013-2019 as it has X, W in the period
2010-2012 and similarly, C shouldn't have any contracts in the years 2010,
2013, 2014, 2015, 2016.
From III, Vendor Y had contracts in
2010 and 2019 and in 2010 D and C hasn't got any contract and A has
already got 2 different contracts from two different vendors => Y has
a contract from B in 2010 => B hasn't got any contracts in 2017,
For Y the only possible contract will be from D => D has got no contracts in the years 2011, 2016, 2017, 2018.
Now, the table looks like:
'N' represents no contract.
Only during 2016, 2017 and 2018, there was only one contract.
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