⌈ x ⌊ x ⌋ ⌉ + ⌊ x ⌈ x ⌉ ⌋ = 1 7 2 9
If the range of positive x satisfy the equation above is α ≤ x ≤ β .
What is the value of 3 0 α + 2 9 β + 1 if we know that it is an integer?
Inspired by: Floor Ceiling Ceiling Floor .
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
Pi Han Goh brings up a valid point. What would the approach be if we are not given that the expression is an integer?
@Pi Han Goh , I had initially intended to show that your problem could be solved this way. But I accidentally typed in the wrong answer, sorry for the inconvenience. The fact that the answer is an integer gives it away.
Log in to reply
If we don't know that the answer must be an integer, how would you determine that 3 0 α + 2 9 β + 1 equals to 1 7 3 0 exactly?
Log in to reply
I know how to solve it otherwise. This was just to show one can solve it without actually finding the values of α , β . Often in JEE, resorting to such tricks can help solve problems easily. I actually wanted to post a solution on your problem, but there were many already, so I decided to put up a problem instead.
Log in to reply
@Raghav Vaidyanathan – Do you want to post a note? Or let me post a note?
Log in to reply
@Pi Han Goh – It was your problem, hence it is only right that you do it.
Log in to reply
@Raghav Vaidyanathan – @Raghav Vaidyanathan , see this note !
Maybe we could prove the hypothesis that the answer will always be equal to the RHS of the floorceilingceilingfloor equation.
@Pi Han Goh Sir , does the equality hold at the upper limit of the range. According to me it should be an open interval on the upper limit.
Log in to reply
@Ankit Kumar Jain – @Pi Han Goh Please do reply (though I know that it has been three years since this problem was posted , it is a long time ..still.)
Log in to reply
@Ankit Kumar Jain – I don't understand your question at all. The claim clearly states that we have to first find α and β .
Log in to reply
@Pi Han Goh – What I mean is that the value of beta doesn't satisfy the equation .
Log in to reply
@Ankit Kumar Jain – That makes no sense. I have to find the range of x first. If β ∗ is not a root of x , then by definition β = β ∗ cannot be true.
Problem Loading...
Note Loading...
Set Loading...
This is the shortest way to solve the problem:
Plugging in integer values for x quickly tells us that 2 9 < x < 3 0 .
Assuming x is not an integer: ⌈ x ⌉ = ⌊ x ⌋ + 1
⇒ ⌊ 2 9 x ⌋ + ⌊ 3 0 x ⌋ = 1 7 2 8
Now, using inequalities and properties of floor function, we have:
1 7 2 8 ≤ 5 9 α < 1 7 3 0
1 7 2 8 < 5 9 β < 1 7 3 0
⇒ 1 7 2 8 < 3 0 α + 2 9 β < 1 7 3 0
Since the answer is an integer, 3 0 α + 2 9 β is also an integer. Therefore, 3 0 α + 2 9 β + 1 = 1 7 2 9 + 1 = 1 7 3 0 .
For a more straightforward and rigorous approach, look at the solution to PI Han Goh's original problem .