The four sentences (labelled 1, 2, 3, 4) given below, when properly sequenced would yield a coherent paragraph. Decide on the proper sequence of the order of the sentences and key in the sequence of the four numbers as your answer.
1. If you’ve seen a little line of text on websites that says something like "customers who bought this also enjoyed that” you have experienced this collaborative filtering firsthand.
2. The problem with these algorithms is that they don’t take into account a host of nuances and circumstances that might interfere with their accuracy.
3. If you just bought a gardening book for your cousin, you might get a flurry of links to books about gardening, recommended just for you! - the algorithm has no way of knowing you hate gardening and only bought the book as a gift.
4. Collaborative filtering is a mathematical algorithm by which correlations and cooccurrences of behaviors are tracked and then used to make recommendations.

Statement 1 says "this collaborative filtering". Here "this" refers to a likely preceding statement which explains about collaborative filtering. While statement 1 is an example of collaborative filtering.
Statement 2 starts with "these algorithms". This doesn't look like an opening statement as it describes a certain algorithm ("these").
Statement 3 is explaining about the flaw in the algorithm
Statement 4 makes for a good opening statement
Statement 41 makes a logical block as the example in 1 refers to collaborative filtering of statement 4
Statement 2 must appear soon after the logical block of 41 as it contains the phrase "these algorithms". While statement 2 explains the problem in the algorithm, statement 3 extends the idea of the problem.

Statement 4 : Introduces collaborative filtering
Statement 1 : Given an example of collaborative filtering
Statement 2 : Speaks about the drawback in the algorithm
Statement 3 : Gives an example of the drawback

Hence the logically coherent order is 4123