A geyser in Yellowstone Park spouts at regular intervals.

I too would have selected D, but since you have wrote its wrong i will give a try by following approach

1) or 2) individually tell us that it spouted 3 times a particular day.

what if it spouted at an interval of 7 hrs? then in a day it spouted 3 times or it can be 8 hrs interval as well.

together the sentences tell us that it spouted at exactly 8 hr interval

well, if i tell you correct, then we obviously know what the answer is. and if i say that you're wrong, it will also be known what the correct answer will be. I want someone who can tell me straight away what's the logic of this question. then i'll post the OA

aaaaah ..... i think i got it now....

by telling that there were 3 spouts in a day... doesnt mean that the interval is 8 hrs....

Actually the interval can range from 8 hrs to 12 hrs..... i gues 8 hr interval is clear ....
for 12 hrs. there could be a spout as 12 midnight (may be minutes after), second at 12 noon and third at 12 midnight .. (minutes beofre) ...s o technocally we can have an interval of 12 hrs also ....

if we have interval of 12 hrs ... in 7 days there'll be 7*24/12 = 14 spouts .... Not suff

But if we know that in two consecutive days.. per day spouts are 3 only .... then the interval is 8 hrs only .. becuase for a 12 hrs interval there'll be only 2 spouts on the next day ...

So answer should be C ... i hope i'm right this time ...

1) Geyser can spout at the intervals of 11 hours: 12:01 am, 11:01 am, 10:01 pm
7*24/11 < 18
Or it can spout in every 8 hour interval.
Insufficient.
2) Same issue as in 1).

Combining 1) & 2) we can tell that it spouted 6 times in 48 hours meaning it could spout little less than 9 hours interval.
7*24/9 > 18

Ok, here's the OE, which I couldn't understand its logic so maybe we could try to understand it together:

From (1), we know that the geyser spouted 3 times in a 24-hour period, so the time between two eruptions is less than 24/2 = 12 hours. As a seven-day period has 168 hours, we know there will be more than 168/2 = 14 eruptions, but we do not know whether there will be more than 18 eruptions. NOT SUFF.

(2) says that the time between two eruptions is less than 12 hours, as did (1). By itself, however, (2) is not sufficient, either. NOT SUFF.

(1) and (2) tell us that there were 6 eruptions in a 48-hour period, so the time between two europtions is less than 48/5. Thus in 168 hours, we know that there will be more than 168*(5/48) = 17.5 eroptions. Therefore, the number of eruptions in a seven-day period tonight at midnight is at least 18. However, we do not know if there will be more than 18 eruptions or exactly 18 eruptions. NOT SUFF.

Answer: E!!!!


I honestly don't understand why it chose to divide 24/2 rather than 24/3.

|--------|-------|

by 2 they mean the difference between 3 eruptions.

It sounds right to me.

About being 12 hrs difference, i think durgesh79 has already explained,
12am -12pm -12am in a day.

but you can't say 12am - 12pm - 12am in a day because once you hit the second 12am, you're no longer in the same day technically. Also, when the question says "beginning tonight at midnight," it doesn't really have to start at midnight, does it? it could still start at any time after midnight, or am I wrong? does the new day start at midnight, which is 24:00, 00:00, or at 00:01 hour? heheh....

ok, let me add something to make it clearer to understand the OE:

"|" represents each spout within 24 hours so:

|---|---|

we have 2 time intervals occurred within the 3 spouts within 24 hours since the statements said that 3 spouts occurred within a day.

In order to get the maximum allowed time intervals between each sprout, we need to divide the 24hrs by the number of intervals, so:
24hrs/2 time intervals = 12 hours

In order to get the minimum allowed time intervals between each sprout, we need to divide the 24hrs by the number of sprouts, so:
24hrs / 3 spouts = 8 hours

The time interval can range anywhere from 8hrs to 12 hrs. The rule of thumb here is that the less is the time interval between each spout, the more spouts can occur. So, in 7 days, we have 7 days * 24 hours = 168 hours.

The maximum number of spouts: 168 / 8hrs = 21 spouts
The minimum number of spouts: 168 / 12hrs = 14 spouts.

So the number of spouts can range anywhere from 14 spouts to 21 spouts within 168 hours, so not eff.!