In class, we discussed that the Septuagint (=LXX) version of Jeremiah is shorter than the Masoretic text (=MT). Read below the text of Jeremiah 10:1-11 as it appears in the LXX versus how it appears in the MT. Do the additions make a significant difference? If so, what difference do they make:
LXX
10 Hear the word that the Lord speaks to you, O house of Israel.
2 Thus says the Lord:
Do not learn the way of the nations,
or be dismayed at the signs of the heavens;
for the nations are dismayed at them.
3 For the customs of the peoples are false:
a tree from the forest is cut down,
and worked with an ax by the hands of an artisan;
4 people deck it with silver and gold;
they fasten it with hammer and nails
so that it cannot move.
5 Their idolsa are like scarecrows in a cucumber field,
and they cannot speak;
they have to be carried,
for they cannot walk.
Do not be afraid of them,
for they cannot do evil,
nor is it in them to do good.
9 Beaten silver is brought from Tarshish,
and gold from Uphaz.
They are the work of the artisan and of the hands of the goldsmith;
their clothing is blue and purple;
they are all the product of skilled workers.
*vs. 11 is found in the LXX but may also be a later addition
MT
10 Hear the word that the Lord speaks to you, O house of Israel. 2 Thus says the Lord:
Do not learn the way of the nations,
or be dismayed at the signs of the heavens;
for the nations are dismayed at them.
3 For the customs of the peoples are false:
a tree from the forest is cut down,
and worked with an ax by the hands of an artisan;
4 people deck it with silver and gold;
they fasten it with hammer and nails
so that it cannot move.
5 Their idolsa are like scarecrows in a cucumber field,
and they cannot speak;
they have to be carried,
for they cannot walk.
Do not be afraid of them,
for they cannot do evil,
nor is it in them to do good.
6 There is none like you, O Lord;
you are great, and your name is great in might.
7 Who would not fear you, O King of the nations?
For that is your due;
among all the wise ones of the nations
and in all their kingdoms
there is no one like you.
8 They are both stupid and foolish;
the instruction given by idols
is no better than wood!
9 Beaten silver is brought from Tarshish,
and gold from Uphaz.
They are the work of the artisan and of the hands of the goldsmith;
their clothing is blue and purple;
they are all the product of skilled workers.
10 But the Lord is the true God;
he is the living God and the everlasting King.
At his wrath the earth quakes,
and the nations cannot endure his indignation.
11 Thus shall you say to them: The gods who did not make the heavens and the earth shall perish from the earth and from under the heavens.
Old Testament as Lit 
There is indeed a significant difference between the two versions of the text.
In the first text, it states, “Thus says the LORD…ect” and as the reader we may assume that everything stated is the word of the LORD. However, in the second instance opposite the Septuagint, it seems that the passage switches voices, first we hear from the LORD or a reiteration of what the LORD has said, however the voice appears to switch over to the prophet or the scribe from verse 6 continued. This is a significant difference because in the LXX 10:9 is the same as MT 10:9 but in the former we assume verse 9 is the word of the LORD, while in the latter it is clearly someone else speaking. This might lead readers to confusion. Those that read the LXX will believe something slightly altered from those that read the MT.
The additions made to the Septuagint make a huge difference. While the Septuagint version clearly says that the idols of other nations are worthless and that they have no power, it does nothing to describe the God of Israel. The Masoretic version creates an image of God in addition to an image of the idols of other nations. The two images differ drastically from each other. The idols of the other nations are static, immobile, and man made. The image created of God is one of a God who is living and has influence over other nations and over the earth itself. By reading the Masoretic version you are exposed to the idea that not only are the idols of other nations powerless, but that the God of Israel is all powerful. The Masoretic version, because of its additions, is a fuller version.
The biggest change between the two texts is the emphasis on the Lord. In the Septuagint, the writing is much more straight forward, and it is as if God is talking. In the Masoretic text, Gods word is interjected with many descriptions of the kind of God he is which in my mind makes the flow of the writing more disjointed. It is much easier to understand the Septuagint because there are no breaks in what the Lord says however, you don’t get much of an idea of what this God is that is speaking. I think the Septuagint is a better text if a person is foreign to the God of Israel but if the audience understands who God is, the Septuagint is much clearer about his message.
In the Septuagint version, the reader is given the impression that the Lord is speaking throughout the entire passage. However, in the Masoretic text it becomes clear that the Lord is speaking in the beginning, but that the rest of the text is finished out by the scribe.
It is clear in the first version that the LORD is speaking and in the second one you know it is Him in the beginning, but towards the end you get the feeling that it is someone else. I don’t think the difference between the two is huge, but it is slightly significant. All in all the main point is the same for both: don’t worship false gods.
Verse 6 in the Masoretic Text is a great way to signify the difference. Like others have said repetitively, the emphasis is much more focused on the power of God. Quite simply, the LXX (as we learned is the Greek translation) is not so much focused on God mainly because of the base fact that is is Greek. Greeks don’t want to put so much emphasis on a one superior power that is God, rather they are more concerned with the ability to get a message out to the people. The Masoretic Text, Hebrew translation, is based on a historical representation of the centrality of a single YHWH. Therefore, the message that translation is going to be more focused on the power of God.
The masoretic text has a little more “brown-nosing” for God. The LXX gets to the same point, but does not include the short phrases of praise and has a more direct way of conveying the same message.