As n ranges over all real values in the interval [ 0 , 1 0 0 ] , how many values of n are there such that 4 n + 1 is an odd integer?
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"4n+1" is always odd whatever the the value of "n". our boundary for "n" is 1 to 100.so there are 100 values of "n" for which "4n+1" is odd..... the answer should be 101..... do correct me if I am wrong.... where is the problem..... ???
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The problem is that nonintegers can work too. For example, n = 2 1 gives 4 n + 1 = 3 , which is an odd integer.
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u re goood
There are infinite real numbers n between 0 and 100 that satisfy the question.. what's about 17/2?
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@Andrea Virgillito – well actually, only multiples of 1/2 satisfy this question and as you know, there are 201 multiples of 1/2 from 0 to 100 inclusive.
Naming the variable "n" may not have been the best letter to use for this problem. It is common practice for "n" to be an integer. I think that may have threw you off, Anom.
Also, 4 n + 1 isn't always odd. For example, n = 4 1 gives 2 as the result, and 4 1 is included on the interval given.
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Also, 4 n + 1 isn't always an integer. For example, n = 0 . 1 , 1 . 1 1 . . . , e , e t c . because if n is in real number, 4 n is also in R. And we can say that 4 n + 1 is in R.
rite anom..... plz Daniel elaborate
Yes I agree with you.. All the vales of "4n+1" would be odd, and so the answer should be 101.
daniel, could you give some tips on how to think like this.Or to produce insightful solutions?
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I thought all "real" so I thought only the real numbers, my answer is 101.
Good explanation, thanks!
Nice solution!
This is elegancy
What an elegant answer Daniel! Hats off to you
it has not stated that n is integer or a rational no..
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No it states that n is a real number. That's why Daniel can use a continuous and monotonous function. On that line only rationals (0/2, 1/2, 2/2 etc) satisfy the condition and he rationals are a subset of the reals.
Simply stated: For each whole number from 0 to 100 the result is odd. Count 101.
For n=.5, 1.5, 2.5... 99.5, the result is also odd. Count 100.
For any other value of n, n, 4n an 4n+1 all result in a fraction, not an odd number. Count = 0.
So... 101 +100 = 201. The answer.
It says n is real, not an integer, so it's not 101, it's 201.
As
n
ranges over all real values in the interval
[
0
,
1
0
0
]
, we need to find out for how many values of
n
is
4
n
+
1
an odd integer.
For
4
n
+
1
to become an integer,
4
n
needs to be an integer.If
n
is an integer then definitely
4
n
is an integer since multiplication of integers follows the closure property. We know that,
2
∣
4
⇒
2
∣
4
n
Thus
4
n
is an even integer. But when we add
1
to
4
n
it becomes an odd integer i.e;
2
∤
4
n
+
1
So, every integer of the form
4
n
+
1
is an odd integer, where
n
ϵ
Z
.
In the interval
[
0
,
1
0
0
]
, there are
1
0
1
integers, thus there are
1
0
1
odd integers of the form
4
n
+
1
in this interval.
But, as
n
ranges over all real values in the given interval,
4
n
can also be an integer when
n
is of the form
4
4
k
+
1
,
4
4
k
+
2
or
4
4
k
+
3
for some
k
ϵ
Z
.
Now we need to find out of these three type of real numbers how many give us an even integer for
4
n
. Since if
4
n
is even then only
4
n
+
1
will be odd.
C
a
s
e
1
:
4
×
4
4
k
+
1
=
4
k
+
1
It is an odd integer since
2
∤
4
k
+
1
.
C
a
s
e
2
:
4
×
4
4
k
+
2
=
4
k
+
2
=
2
(
2
k
+
1
)
It is an even integer since
2
∣
2
(
2
k
+
1
)
.
In this problem the value of
n
i.e
4
4
k
+
2
should be in the inteval
[
0
,
1
0
0
]
.
There are 100 such real numbers ranging from
2
1
to
2
1
9
9
.
Thus in this case we get
1
0
0
odd integers of the form
4
n
+
1
in the given interval.
C
a
s
e
3
:
4
×
4
4
k
+
3
=
4
k
+
3
=
2
(
2
k
+
1
)
+
1
=
2
k
′
+
1
for some
k
′
ϵ
Z
.
It is an odd integer since
2
∤
2
k
′
+
1
=
2
∤
4
k
+
3
Thus, there are no even integers in this case also.
Therefore there are a total of
1
0
1
+
1
0
0
=
2
0
1
Thus there are a total of
2
0
1
odd integers of the form
4
n
+
1
when
n
ranges over all real numbers in the interval
[
0
,
1
0
0
]
.
It says n is real, not an integer, so it's not 101, it's 201.
4 n must be an even integer since even + odd = odd
4
n
= 2
k
n
= 0.5
k
where
k
is an integer with interval [0,200]
There are 201 numbers from 0 to 200
Therefore, there are 201 values of n such that 4 n + 1 is an odd integer
N=1/4. 4n+1=1. So your solution is not correct.
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Nevermind. My Bad.
4n+1 = 2 when n=1\4
Nope. For n=1/4, 4n+1=2 (which is even!)
It's from 0 to 100, not 200
most helpfull among all
n ranges between 0 and 100, so 4n+1 ranges between 1 and 401, and there is 201 odd integer in this interval!
Good explanation. The trick here is that n need not be an integer.
Very elegant and concise solution. I worked out that if n was an integer 4n + 1 would be odd and that if n ended in .5 4n+1 would also be odd and that there were 201 values that fitted these criteria (101 integers and 100 intermediate values).
We know that 4 n + 1 has to be an integer. Therefore 4 n must be an integer. For that to happen, n has to be at least a rational.
Being an odd integer, means that 4 n + 1 = 2 k + 1 , where k ∈ Z . Isolating n gives us n = 2 k .
Now, because 0 ≤ n ≤ 1 0 0 , 0 ≤ k ≤ 2 0 0 . Counting every integer that is between 0 and 200, reveals 201 possible k s.
Therefore, there are 201 possibles values of n in [ 0 , 1 0 0 ] that holds the property.
An easy approach is checking from the end results (4n + 1) The range of results will be from 1 (4 * 0 + 1) and 401 (4 * 100 + 1)
We can then rephrase the problem to: How many odd integers are there between 1 and 401 inclusive. This can easily be calculated with Round down[(n+1)/2].
The number of odd numbers from 1 to 401 is Rounddown[ (401+1)/2 = 201
Please do note that this is possible because we have the values of n as any real number between 0 and 100 inclusive. If we were restricted to integers we would be unable to get values such as 3, 7, 11, 15... which are the results of n being non-integer (1/2, 3/2, 5/2...)
The values of n satisfying the condition are
0/4, 2/4, 4/4, 6/4, ......., 400/4
So there are 400/2 + 1 no. of values of n satisfying the condition.
So there are 201 possible values for n.
All odd integers are in the form 2 k + 1 , for some integer k . So, if 4 n + 1 is an odd integer, there must exist some integer k 0 such that 4 n + 1 = 2 k 0 + 1 . Solving for n , we get n = 2 k 0 . Thus, the values of n we want are exactly those that are one-half of an integer. In the given range, there are 2 0 1 possible values of n , specifically 2 0 , 2 1 , 2 2 , … , 2 2 0 0 . □
If 4 is multiplied by a number of the form 4 2 k − 1 , you'll get 2 k − 1 + 1 = 2 k , which is not odd. That means that the numerator must be even, and then the fraction will be expressed with 2 as the denominator. 1 0 0 = 2 2 0 0 . That means that for the numerator, we can choose all the numbers from 0 to 2 0 0 . In this interval there are 2 0 1 numbers. Hence, the answer is 2 0 1 .
Every integer from 0 to 100 works, as 4n is an even number and + 1 makes it an odd integer. Furthermore, every half also works from 0.5 to 99.5 , which is another 100 values. Thus , there are 101 + 100 values that make it odd.
Yes. Those are the cases in which the numerator is divisible by 2 .
Let n be of the form n=
4
k
The range of n is [0,100] so the range of k is [0,400]
This implies 4n+1=k+1
So for all even values of k, 4n+1 is odd.
So the possible values of k are 0,2,4,......,398,400.
Therefore there are 201 values of k possible.
Therefore there are
201
values of n possible.
If 4 n + 1 is an integer, 4 n is an integer too, so n must be equal to a rational number q p where q ∣ 4 ( q divides 4 ). If q = 4 , 4 n + 1 = p + 1 so p must be even, therefore simplifying p with q , the fraction will have denominator 2 . If the fraction has denominator 2 , 4 n + 1 = 2 p + 1 , so it will be odd for each p integer; if 0 ≤ n ≤ 1 0 0 and n = 2 p , 0 ≤ p ≤ 2 0 0 , thus p can assume 2 0 1 integer values. In this are also included integer values of n , when p is even.
Note that n is a real number in the range [0,100]. 4n+1 odd <=> 4n even <=> 2n is an integer. So n can be 0, 1/2, 1, 3/2, ..., 100, these are 201 values.
4n+1, is an odd integer, means 4n is even,
which in turn means 4n/2 = 2n is any
integer. This further means n can be any
integer k, from 0 to 100 (101 possible
values), as well as k/2 for each k.
So k together with k/2 can have 201
possible values for n (note for k =0, k = k/2).
4n+1 is itselft odd with any +ve integer value. so, from 0 to 100 are solutions and 1/2,3/2, 5/2, ......, 199/2 satisfy. so there are all 201 solutions............
All the values of n such that n=x/4 where x is even satisfies the condition.
Since n is less than or equal to 100, x should be less than or equal to 400.
So the numbers 0/4, 2/4, 4/4, 6/4 ......400/4 satisfies the condition and the number of terms can be easily found using the concept of arithmetic progression
for 4n +1 to be an odd integer, 4n has to be an even integer.
For n=an integer, all 101 values from [0,100] will satisfy, moreover even the values of the form z+ 0.5, where z is an integer, will be 4z+2 when multiplied by four and thus will be even.Thus we have another 1 set of values, satisfying us. Thus the total no. of values will be 100+ 101=201
0 to 10.5 containing 22 numbers at an interval of 0.5, 11 to 20.5, 21 to 30.5 ... so on till 81 to 90.5, 91 to 100 so basically it is 22+20 *8 times and 19 for the last number line. is 201
If 4 n + 1 must be an odd integer, then 4 n must be an even integer.
For n ∈ [ 0 , 1 0 0 ] , 4 n ranges from 0 to 4 0 0 , inclusive. There are 2 0 1 even numbers in the range [ 0 , 4 0 0 ] , so there must be 2 0 1 corresponding values of n between 0 and 1 0 0 , inclusive.
First observe that 1 is an odd integer where n is chosen to be 0. Next observe that 401 is an odd integer where n is chosen to be 100. Every odd integer between 1 and 401 can be expressed in the form 4n+1 where n is a real value in (0, 100). Therefore this question is equivalent to counting the number of odd integers in [1, 401], which is simply just (401+1)/2 = 201.
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Let f ( n ) = 4 n + 1 . Note that f ( n ) is continuous and monotonically increasing (never decreases). Also, f ( 0 ) = 1 and f ( 1 0 0 ) = 4 0 1 , so every odd number from 1 to 401, inclusive, is achieved exactly once for n in the interval [ 0 , 1 0 0 ] . This is 2 0 1 values.