question,for 1st question ans may be 35....
because -1 to 5(inclusive),right than {-1,0,1,2,3,4,5} total element in set 7 so that makes 7c3=7!/(4!3!)=35
i may be wrong but plz check ans

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Hard from the best resources numeric entry https://gre.myprepclub.com/forum/numeric-e ... %5B%5D=117

Medium https://gre.myprepclub.com/forum/numeric-e ... %5B%5D=117

regards

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