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[grettlin2]

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Hi, I can't figure out why the answer it is from Barron's exam A.

Question 1:
Kate has six different books. Assuming the order of selection doesn't matter, how many ways can Kate select, from these six books, two different books? (answer is "15")

=> however, I think it should be 30?
because first time, he can have 6 books to choose; second time, there are only 5 books left. So, 5 x 6 = 30. Am I wrong?

Question 2:
Why sin (TT/3) equals sin (2TT/3)?

=> can't figure out why.....

Thanks for the help!

 

[w3chen99]

Remember that order doesn't matter, so multiplying 6x5 would not work....


This is a visual breakdown
e.g. 6 books A-F

A B C D E F

AB
AC
AD
AE
AF
BC
BD
BE
BF
CD
CE
CF
DE
DF
EF

15 choices (5+4+3+2+1)

 

[grettlin2]

Hi w3chen99, thanks a lot! Know I can see why.... 🙂

 

[KenFred]

The actual mathmatical calucaltion would be:

(N!)/((N-k)*k!) n=6 and k=2 in this case

(6!)/(4!*2!)=15

Total possibilities is 720. 6*5*4*3*2*1

You then have to compensate for the number you will be taking which is 2

Hope this helps.

 

[jjflynn2]

DO you recall exactly how the second math problem was worded?
Did the problem refer to the quadrant of each?

 

[HSO]

when order of selection (order) matters, then u use the permutation formula which is N!

when order of selection doesn't matter then you use the combination formula: N!/K! (N-K)! Where K is the "lesser" number and N is the "greater" number in the problem.

Hope this helps.

 

[grettlin2]

Hi guys, really appreciate for your help! I know there is a equation (formula) to calculate this type of problems, but I can't remember. Thank you for providing me the detail answers. Thanks!

BTW, if it is possible, could you help me why sin (Pi/3) = sin (2pi/3)
? Quite confuse.....

 

[zero_cool_ck]

sin is positive in first and second quadrant.

pi/3 = 60 degrees first quadrant, hence, sin 60 deg. = sq.roo(3)/2

2pi/3 = 120 degrees. hence, in second quadrant. therefore, sin theta will be positive. in second quadrant, the angle between the - x axis and the arm will be still 60 degrees. hence,

sin 120 deg. = sin 60 deg. = sq.rt(3)/2

hope this helps.

 

[KenFred]

I have yet to study or even see the DAT test. Are these questions actually on the DAT?

What type of math questions are on the test? Basis math, or is calculus?

 

[aphistis]

No calculus, not even close. More like first-semester algebra.

 

[critterbug]

.....with a little trig thrown in 😉

 

[ItsGavinC]

But I really lucked out and had NO trig -- not ONE single question! No exaggeration here, my problems were completely simple, which was a blessing since I was freakin' out about the math section.