2 exprs from 4 can be selected in 4P2 = 12 ways
now only possibities where the product is of the form
x- (by)^2
are (x+y)(x-y) & (x-y)(x+y) = 2 possibilties
so reqd P = 2/12 =1/6
Hope this is clear
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Source: Beat The GMAT — Problem Solving |
2 expresion picked from another 4 = 4!/[(4-2)!*2!] = 6
The only expresion that results in a x^2-(by)^2 form is (x+y)*(x-y), there is no way to say that (x-y)*(x+y) is another way since multiplication is a conmutative operation.
The only expresion that results in a x^2-(by)^2 form is (x+y)*(x-y), there is no way to say that (x-y)*(x+y) is another way since multiplication is a conmutative operation.
Well both will do here even if u use Combinations, then also u will get the same result.
Regards
Samir
Samir
Hey Samir
Sorry but this is not clear to me.
4P2 = 12 ways but 4C2 = 6
Now you have said that possibities where the product is of the form
x- (by)^2
are (x+y)(x-y) & (x-y)(x+y) = 2 possibilties
so reqd P = 2/12 =1/6
If you use combination then the ans would be 2/6 = 1/3 instead of 1/6
Aorry for the repeated question. As always thanks in advance for your help
Sorry but this is not clear to me.
4P2 = 12 ways but 4C2 = 6
Now you have said that possibities where the product is of the form
x- (by)^2
are (x+y)(x-y) & (x-y)(x+y) = 2 possibilties
so reqd P = 2/12 =1/6
If you use combination then the ans would be 2/6 = 1/3 instead of 1/6
Aorry for the repeated question. As always thanks in advance for your help
If we use Combinations then favorable outcome will be only
(x+y)(x-y) = 1 outcome as order would not be important, we can use it here coz multiplication works both ways
so it will be 1/4C2 = 1/6
(x+y)(x-y) = 1 outcome as order would not be important, we can use it here coz multiplication works both ways
so it will be 1/4C2 = 1/6
Regards
Samir
Samir
I figured this out today as well (semi-guessed, but got it right). Anyway, I apologize for probably stupid question, but what does this mean??? What are P and C in these:
4P2 = 12 ways but 4C2 = 6
4P2 = 12 ways but 4C2 = 6
Yuri, it is short-form notation for PERMUTATION and COMBINATION calculations.yuri wrote:I figured this out today as well (semi-guessed, but got it right). Anyway, I apologize for probably stupid question, but what does this mean??? What are P and C in these:
4P2 = 12 ways but 4C2 = 6
For example: 4C2 = "Four choose 2" = 4!/(2!2!)
