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shrive555
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Fish in tanks 13 Sep 2013, 12:51
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You have a fish tank that has 100 fish in it right now. 5 fish die each day. Every day, 9 fish are born. How many days will it take for the tank to have 200 fish?

how do we setup equation for this.

PS: i don't know if that question is previously asked.

Thanks



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Fish in tanks 13 Sep 2013, 14:52
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shrive555
You have a fish tank that has 100 fish in it right now. 5 fish die each day. Every day, 9 fish are born. How many days will it take for the tank to have 200 fish?

how do we setup equation for this.

PS: i don't know if that question is previously asked.

Thanks
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Dear shrive555

I don't know that this would be a GMAT level question, but I am happy to help. :-)

Each day, 5 fish die and 9 or born, so that's a net change of (-5) + 9 = +4. Sometimes, with questions like this, we might have to worry if the number were going to drop below zero. I guess it's also ambiguous whether the nine being born happens before the five die ---- there's no info about that in how you stated the question.

Assuming we are just interested in end of the day counts, then how many net changes of +4 would be between 100 and 200? That would be (200 - 100)/4 = 25 day. In 25 days, the count at the end of the day would be 200.

Suppose the 9 were born in the morning, the 5 died in the evening --- then, each day, the tank would go up 9, then down 5. On Day 23, the count would finish at 192. Then, on the 24th day, the count would go up to 201, topping 200 for the first time, then come back down to 196. Then on Day 25, they would go back above to 205, and finish at 200. That's only if the addition of 9 clearly comes before the subtraction of 5, but again, we have no reason to assume that from the question.

I hope all of this helps.
Mike :-)
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Fish in tanks 14 Sep 2013, 08:04
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mikemcgarry
shrive555
You have a fish tank that has 100 fish in it right now. 5 fish die each day. Every day, 9 fish are born. How many days will it take for the tank to have 200 fish?

how do we setup equation for this.

PS: i don't know if that question is previously asked.

Thanks
Dear shrive555

I don't know that this would be a GMAT level question, but I am happy to help. :-)

Each day, 5 fish die and 9 or born, so that's a net change of (-5) + 9 = +4. Sometimes, with questions like this, we might have to worry if the number were going to drop below zero. I guess it's also ambiguous whether the nine being born happens before the five die ---- there's no info about that in how you stated the question.

Assuming we are just interested in end of the day counts, then how many net changes of +4 would be between 100 and 200? That would be (200 - 100)/4 = 25 day. In 25 days, the count at the end of the day would be 200.

Suppose the 9 were born in the morning, the 5 died in the evening --- then, each day, the tank would go up 9, then down 5. On Day 23, the count would finish at 192. Then, on the 24th day, the count would go up to 201, topping 200 for the first time, then come back down to 196. Then on Day 25, they would go back above to 205, and finish at 200. That's only if the addition of 9 clearly comes before the subtraction of 5, but again, we have no reason to assume that from the question.

Thank you
I hope all of this helps.
Mike :-)
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Thank you Mike for being generous :-)



Archived Topic
Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
Where to now? Join ongoing discussions on thousands of quality questions in our Quantitative Questions Forum
Still interested in this question? Check out the "Best Topics" block above for a better discussion on this exact question, as well as several more related questions.
Thank you for understanding, and happy exploring!