reto wrote:
milind1979 wrote:
If b is the product of three consecutive positive integers c, c + 1, and c + 2, is b a multiple of 24 ?
(1) b is a multiple of 3,
(2) c is odd.
Dear Community
How do not run the risk that when testing both statements together (multiple of 3 and c is odd):
1 * 2 * 3 = 6 > Answer NO
3 * 4 * 5 = 60 > Answer NO
5 * 6 * 7 = 210 > Answer NO
If one is under time pressure, one would stop here and come to the conclusion that together 1+2 are sufficient. However its not.
Is it just about plugging in one more > 7 * 8 * 9 or is there a way, which tells me that i should not stop after three plug in's?
Thanks
Hi Reto,
When you try to plug numbers. You need to pick smart numbers that work. However, knowing some rules is really beneficial such as consecutive numbers rules. When I solve the problem by plunging numbers I will do the following ( I will detail my thoughts to help you):
Statement 1: b is a multiple of 3
C=1 ......> 1*2*3= 6 multiple of 3.........Answer to question NO
C=2.......> 2*3*4=24 multiple of 3 &24 Answer to question YES
Statement 1 is Insufficient.. then you can go to examine to statement 2. However, I would not use C=2 in my plug-in process because when you see Statement 2 it gives me impression (comes from practice) that you can focus your effort to look for other odd numbers. look to 24. it is easy to infer that any 3 consecutive number containing 24 will be multiple of 24 So choose C=23.......> 23*24*25 is multiple of 24... Answer to the question YES
So we reached same result Statement 1 is Insufficient with 2 odd numbers
Statement 2: c is odd.
When you look to you work above with C=1 & C=23. Statement 2 is Insufficient
Combining 1+2, C=odd number & multiple of 3, then look to your work above .........both are Ins.... Answer is E.
Another alternation is to start with Statement 2 with smart numbers also near 24 and then look into Statement 1.
I hope it helps