manchester grammar 2014 maths question

[Ahins]

I am stuck on this question. I would appreciate some help on this:

Each day a shoal of small fish increases in number by 50% but each night s shark eats 300 of them. So if there are 1000 fish on Monday morning, then there will be 1500 by Monday evening but only 1200 left by Tuesday morning!

Q: If the number of fish each morning is the same on each of the four days, how many fish were there on Monday morning?

I know there is a number to start off with on Monday say X
and there is the 1.5of X increase by night, with 300 eaten over night
so on Tuesday morning we should have 1.5X- 300.

I am sure there being the same number every morning is significant but i cannot link that fact with the expression above to find X.

PS- trying to think logically as well rather than using algebra but I am not getting it

Help please!

[Guest55]

Have a think .... what the shark eats must be the same as the 50% increase.

[Ahins]

ok so struggling with the thinking, but I can see your point. So how do I proceed to find the original number of fish based on the information I am given? What are the logical steps?

Thanks.

[Guest55]

We know 50% of the amount - so just double it.

[Ahins]

Thanks for the response. But do we know the amount? 300 is what is eaten every night. How does this relate to the original amount? I am really missing something!

[Guest55]

50% of the amount is 300 ...

So 100% is ....

[leanmeamum]

300 is 1/3 of total in the evening before the shark eats them