DS Question

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Posted by: vik76gosai

1. A certain list consists of several different integers. Is the product of all the integers in the list positive?

(1) The product of the greatest and the smallest of the integers in the list is positive
(2) There is an even number in the list.

2. Is the integer n multiple of 15?
(1) n is multiple of 20
(2) n+6 is multiple of 6


3. The child selected d a three-digit number, XYZ, where X, Y and Z denote the digits of the number. If no two of three digits selected were equal, what is the three-digit number?
(1) The sum of the digits was 10
(2) X<Y<Z

1 Q)
1) the integers can be either all positive or all negative, zero is excluded. first isn't suff, since it can br negative if the number of integers is odd and positive if it's even
2) second is not suff, just consider numbers -1 and 2 - negative, 1 and 2 - positive, 0 and 2 - neither negative, nor positive
together they are suff

2 - Q) together they are suf

3 - Q) together are not suff, consider numbers 235 and 145 - you should quickly understand that Z can not be more than 5, Y be less than 5, and X less than 4. then attack the question with different combinations of digits

can you please explain number 2. Why are both sufficient

2. Is the integer n multiple of 15?
(1) n is multiple of 20
(2) n+6 is multiple of 6
to be a multiple of 15, an integer must have factors 3 and 5. From the first premise we know that n has a factor of 5 (20/4=5). from the 2nd premise we know that n has a factor 3 (6/2=3). Though each alone isn't enough, both give us n which divides both by 3 and 5, thus it must be a must be a multiple of 15

ahh....thank you very much, that makes sense.