QUESTION TYPE: Sufficient Assumption
CONCLUSION: More etching tools are used for engraving than are not used for engraving.
REASONING: All pin tipped tools are used for engraving. Some bladed tools are used for engraving and some are not. All etching tools are pin tipped or bladed.
Note: This situation may be confusing. I’ve drawn a diagram to illustrate this question. The key to this question is we don’t know how many bladed tools are used for engraving and how many aren’t:
So category 3 (bladed, not engraving) could be enormous. Way bigger than categories 1 + 2.
ANALYSIS: This argument ignores quantities. There could be three types of pin tipped tool, and 3,000,000 types of bladed tools. And maybe only 2 bladed tools are used for engraving. That would mean 5 tools are used for engraving and 2,999,998 are not.
We need to eliminate this possibility. For instance, by saying there are equal numbers of pin tipped and bladed tools, or more pin tipped tools.
- This tells us that there are no chiseling tools used for engraving (for example). And no hammering tools used for engraving. So what? The conclusion is only about etching tools. Etching tools are only pin tipped or bladed
- CORRECT. This equalized the numbers of both tools. It makes it mathematically certain that most etching tools are used for engraving. Let’s say there are 8 pin tipped tools and 8 bladed tools. Then at least nine would be used for engraving: 8 pin tipped, and at least one bladed.
- This answer isn’t a sufficient assumption. It just tells us a useless fact about pin tipped and bladed tools. Look at my example in the analysis section. I was already assuming the two categories didn’t overlap, yet the conclusion wasn’t true in my example.
- This weakens the argument! We want to prove that etching tools are used for engraving.
- We actually already knew this. Pin tipped tools are all used for engraving, and pin tipped tools are the only etching tools that aren’t bladed.
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