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I was banned from answering to some riddles, but I can still post them :)

OK, my riddle about hungry cows:

Imagine that on a meadow there are 40 cows, and they are able to eat the whole grass within 20 days. But if there are 30 cows, they will eat grass within 30 days. Please, tell me how many days will need 25 cows to eat a grass from this meadow? :)

Tags: riddle

Views: 315

Replies to This Discussion

I love this riddle because I can't figure it out. Nevertheless, I bet I'll answer it  before jean :-)

Hi Saed,

You indeed answered before I did. ;o))

I'm no math specialist and I was lucky in my answer to your riddle.

I'm not that sure about my answer this time as well. The only thing I'm sure about is that these cows wouldn't have stayed more than a half, had they been on a soccer pitch facing a decent team!






I guess in this modern era, cows eat fast food instead of grass. That's why I can't solve this riddle :-)

Maybe other cows prefer fast foods, but my cows like eating green grass :)

Hello Joanna,

My level in maths is near 0.
So, I'm very sorry but I'm totally unable to answer this riddle.
I still will follow the answers to see if I can eventually understand a bit of it...
And when I have time, I will go and see your maths explanations, it won't be unnecessary !

Thank you and take care

Sorry, but I don't like this type of answers.

You gave up without any try, grrrrr.

My calculations yielded to two answers: 42.9 days or 67.04 days and I guess 42.9 days is correct. Is it?

I guess 42.9 days is correct.

Sorry, this is not a correct answer :)

Try again.

Hello, Joanna,

Let us know the average speed of cows' eating:

There are 70 cows: 40 + 30 = 70.

There are 50 days: 20 + 30 = 50.

So, the average speed is: 70 : 50 = 1,4 (days). One cow can eat the grass in 1,4 days.

25 cows will need 35 days to eat all the grass from the meadow:

1,4 x 25 = 35 (days) 

??? :):):) I'm not sure we can divide cows by days in order to find the average speed... But other quantities are unknown :) 

Interesting way of solving this riddle, but sorry to say, your answer is not correct.

Please, don't give up and try again :)

My answer is also 35 days.


[I'm so happy when I see lots of answers for the same question; it tells me I may be wrong (or I may be right), but either way is OK.  At least I won't have to feel too silly about it!]

This was my thinking.

40 cows

30 cows

25 cows

[40 - 30 = 10.  30 - 25 = 5.  Pattern = difference of 10, difference of 5]


20 days

30 days

__ days

[difference between 20 and 30 = 10, so difference between 30 and ___ will be 5 (following same pattern of difference 10, difference 5]

Logically, this makes sense to me. 

more cows (40), same pasture, fewer days (20)

30 cows, same pasture, 30 days

25 cows, same pasture, more days (35)

~ ~ ~

Because we have the 30 cows / 30 days even measurement to 'balance' from, to work from, this makes sense to me.

But then I think...

I also imagine a similar situation using something more familiar or relevant to me.

Imagine being a group leader, 30 kids, a paper they have to erase markings from, 30 minutes for them to complete the project.

Imagine 40 kids = could finish faster.

Imagine 25 kids = would take them a bit longer to finish.

So I think my answer makes sense.

~ ~ ~

I think if there were 15 cows, the answer would be 45 days.

Am I a total dunce?  Does my thinking make sense to you?  Why or why not?



Wow, your way of thinking is amazing, and makes sense to me :)

And it would be correct but unfortunately grass on the meadow is still growing.

When kids have erased markings from the paper nothing new appear on this paper, when you cut grass, the next day you will see that it will grow and grow. :)

But you are close to the correct answer :)


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