danzig wrote:
Karishma,
I don't understand this part of your explanation:
"Notice that 5, 7, 11 and 13 are primes and none of their multiples are in either set. So ignore them. We just need to focus on 2 and 3 of set A and 2, 4 and 6 of set B."
Why do we have to do that? Thanks!
This is part of your step 2: Remove the products that appear more than once.
The logic here is that a product involving 5/7/11/13 will not appear more than once. So we ignore these numbers.
Say we select 5 from A. Now, when we select any number from set B, we get a distinct product i.e. we get 4 distinct products (5*2, 5*4, 5*6, 5*13)
Now think, can you select a number other than 5 from set A and some number from set B to make one of these 4 products? i.e. Without selecting 5 from set A, can you make a product of 10 or 20 or 30 or 65? No, because to make 10/20/30/65, you need a 5 but you have no other 5 or multiple of 5.
Same is the case with 7, 11 and 13 (primes that appear only once in one set). So the products made by these prime numbers will not appear more than once.
You don't really need to think all this during your test. Lots of practice and thorough analysis will make these things intuitive.
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