Re: GRE Math Challenge #1- Below are some tough word problems
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27 Jan 2026, 06:15
1) Set - [ -1,0,1,2,3,4,5]
Number of unique -ve products -
exclude 0 cuz we need -ve product using 3 numbers. we now have 6 numbers - -1 , 1, 2, 3, 4, 5
examples of the products :
-1*1*2
-1*2*2
.
.
.
.
.
.
.
.
.
so we have 5P2 such numbers which is = 10
number of unique positive products -
we need to choose 3 out 5 numbers
meaning
5C3 = 10
and we have 0 as a unique product
therefore 10+10+1 = 21 unique products
2) we have 2 ,3 , 5 and 7 as our prime numbers in 0-9
that is, 4 prime numbers
so number of combinations is 4*4*4 (since its not explicitly mentioned that no repetitions are allowed) = 64 possible combinations
P( 252 being the code) = 1/64
3) 3 doctors need to be selected from 6 doctors and those 6 doctors need to be chosen from the 12
basically we need to choose 3 from 12 ; 12C3 = 220