Number series

I think this kind of question isn't always bad. It can teach thinking in different ways, and it can also reward perseverance.

And if the question is marked fairly (I accept that often it isn't) then it can illustrate to the class that some questions can have several, or even infinite, valid answers.
@Cubist
I would not mind at all a question that asks “Can you find a relatively simple pattern that fits this sequence?” Pattern finding is an essential skill. What I object to is framing such questions in a multiple-choice format that implies whatever pattern X sees is the “correct” pattern.

I see a possible pattern. That calls for investigation, not dogmatism. I greatly doubt that you and I fundamentally disagree on that. I at least have developed hypotheses that turned out on further study to be wrong. Developing hypotheses is good. Recognizing indeterminacy is good. Investigating is good. What is not good is telling students that the student is wrong unless the student guesses what my process was when my process is not unique.

I am all in favor of intuition and creative hypotheses. What got me going in this thread was the implication that alternative hypotheses were excluded by the existence of one plausible hypothesis. I had to deal with too many fiascos created because people grabbed the first solution that solved some aspect of a problem. The last fifteen years of my career mostly involved dealing with problems that never would have arisen if someone had considered whether alternative solutions existed and which alternative was likely to be best under alternative futures.

We teach mathematics in part to teach thinking systematically. I love questions that ask what is possible. I hate questions that imply that an indeterminate answer is apodictically certain.

Ultimately, I suspect that multiple-choice answers, while convenient for grading, are bad for students because they imply a simple dichotomy between correct and incorrect that frequently does not exist.
 
Subhotosh

Some rote learning is necessary. But the essence of cramming is rote learning of formulas for specific types of question typical of standardized exams. No one learns anything permanent from that experience.

The Sumerians had computers with rollerballs rather than keys? Very ingenious. Of course, cuneiform did not adapt easily to a qwerty keyboard.
Abacus was the Apple that we ate!!
 
15+ (a + b^3)

A will start from 1 then increase by 2 .

B will start from 1 and increase by 1 .

This is the pattern.


Whatever polynomial pattern u guys are giving its beyond my capacity right now.
 
15+ (a + b^3)

A will start from 1 then increase by 2 .

B will start from 1 and increase by 1 .

This is the pattern.


Whatever polynomial pattern u guys are giving its beyond my capacity right now.
I started to like the author's ideas of creating these problems. It seems that if we could solve 100 problems of his, we would cumulate all of his ideas. lol

I am just wondering what would happen after that! Would the game be boring??
 
15, 17, 26, 47, 86, ?

A 132
B 149
C 169
What is the pattern
15+ (a + b^3)

A will start from 1 then increase by 2 .
B will start from 1 and increase by 1 .
This is the pattern.

Whatever polynomial pattern u guys are giving its beyond my capacity right now.
Actually, what you are claiming is a polynomial, namely 15 + (2n-1) + n^3 = n^3 + 2n + 14.

But if a cubic works, that would have been discovered.

And in fact, for n=1 we get 17, not 15; you seem to be omitting the first term, 15. (The rest works, and gives the answer 149.)

Where did you get your answer?
 
15, 17, 26, 47, 86

15+ (a + b^3)

A will start from 1 then increase by 2 .
B will start from 1 and increase by 1 .
This is the pattern.
As Dr. Peterson points out, this 'pattern' does not work for the first term.
It gives 17, not 15.

Actually, what you are claiming is a polynomial, namely 15 + (2n-1) + n^3 = n^3 + 2n + 14.


That is why I earlier gave the answer - post #55:

It would appear the answer is B 149;
the presumed, unlikely pattern being [MATH]a_n= 15 + (n-1)^3 +\text{ max}(0,2n-3)[/MATH]which works for all including the first term.
(This was a particularly poor question - when even their own answer doesn't work).
 
@Cubist
I would not mind at all a question that asks “Can you find a relatively simple pattern that fits this sequence?” Pattern finding is an essential skill. What I object to is framing such questions in a multiple-choice format that implies whatever pattern X sees is the “correct” pattern.

I see a possible pattern. That calls for investigation, not dogmatism. I greatly doubt that you and I fundamentally disagree on that. I at least have developed hypotheses that turned out on further study to be wrong. Developing hypotheses is good. Recognizing indeterminacy is good. Investigating is good. What is not good is telling students that the student is wrong unless the student guesses what my process was when my process is not unique.

I am all in favor of intuition and creative hypotheses. What got me going in this thread was the implication that alternative hypotheses were excluded by the existence of one plausible hypothesis. I had to deal with too many fiascos created because people grabbed the first solution that solved some aspect of a problem. The last fifteen years of my career mostly involved dealing with problems that never would have arisen if someone had considered whether alternative solutions existed and which alternative was likely to be best under alternative futures.

We teach mathematics in part to teach thinking systematically. I love questions that ask what is possible. I hate questions that imply that an indeterminate answer is apodictically certain.

Ultimately, I suspect that multiple-choice answers, while convenient for grading, are bad for students because they imply a simple dichotomy between correct and incorrect that frequently does not exist.

After reading this, I think our opinions are aligned! This question shouldn't be given in a pure multiple choice scenario if the student can't show any reasoning on the answer paper. And because it may require some perseverance then I wouldn't like to think this would ever appear in a timed exam. I think it would be better suited for one or two homework questions AND having a follow-up discussion in the classroom.
 
After reading this, I think our opinions are aligned! This question shouldn't be given in a pure multiple choice scenario if the student can't show any reasoning on the answer paper. And because it may require some perseverance then I wouldn't like to think this would ever appear in a timed exam. I think it would be better suited for one or two homework questions AND having a follow-up discussion in the classroom.
I may try to create such a problem that has two relatively simple answers. That could lead to an enlightening discussion in class (if the teacher grasped the thought). Upon looking over this thread, I realized that Dr. Peterson hit the nail on its head in post 2.
 
I may try to create such a problem that has two relatively simple answers. That could lead to an enlightening discussion in class (if the teacher grasped the thought). Upon looking over this thread, I realized that Dr. Peterson hit the nail on its head in post 2.
Fully agreed.

I have lots of experience with this. Here is a blog post of mine about this issue (in the typical American form where "patterns" are relatively simple): Uncertain Sequences

There is a lot of benefit to discussing such puzzles in a classroom setting, where the ambiguity can be the main point, and creativity, rather than correctness, is the goal. What troubles me is that the problems under discussion appear to be used in tests such as the NRA CET (Common Eligibility Test of the National Recruitment Agency), which presumably determines what one can do in life; a good mathematician would likely fail, by refusing to imagine that there is a correct answer! So people study how to "solve" them, which is an utter waste.
 
I think that the OP meant this

[MATH]a_1 = 15[/MATH]
[MATH]a_{n+1} = a_1 + (a + b^3)[/MATH]
Which means [MATH]a_2 = 17[/MATH]
 
15+ (a + b^3)

A will start from 1 then increase by 2 .

B will start from 1 and increase by 1 .
I think that the OP meant this

[MATH]a_1 = 15[/MATH]
[MATH]a_{n+1} = a_1 + (a + b^3)[/MATH]
Which means [MATH]a_2 = 17[/MATH]
I think you meant
[MATH]a_{n+1} = a_n + (a + b^3)[/MATH]​

If so, then
[MATH]a_{2} = 15 + (1 + 1^3) = 17[/MATH]​
[MATH]a_{3} = 17 + (3 + 2^3) = 28[/MATH]​
[MATH]a_{4} = 28 + (5 + 3^3) = 60[/MATH]​

My interpretation made it correct except for the first term. (And, frankly, I was wondering if we'd be told that 15 was the problem number.)

In any case, wouldn't teaching the math surrounding these problems include learning how to correctly write recursive definitions?
 
I think you meant
[MATH]a_{n+1} = a_n + (a + b^3)[/MATH]​

If so, then
[MATH]a_{2} = 15 + (1 + 1^3) = 17[/MATH]​
[MATH]a_{3} = 17 + (3 + 2^3) = 28[/MATH]​
[MATH]a_{4} = 28 + (5 + 3^3) = 60[/MATH]​

My interpretation made it correct except for the first term. (And, frankly, I was wondering if we'd be told that 15 was the problem number.)

In any case, wouldn't teaching the math surrounding these problems include learning how to correctly write recursive definitions?
Dr.Peterson, I meant this

[MATH]a_{n+1} = a_1 + (a + b^3)[/MATH]
[MATH]a_1 = 15[/MATH][MATH]a_{2} = 15 + (1 + 1^3) = 17[/MATH][MATH]a_{6} = 15 + (9 + 5^3) = 149[/MATH]
 
Okay I have This number series
3,9, 24, 57,?, 267, 552.



Options:

121,118,114,126.
 
Dr.Peterson, I meant this

[MATH]a_{n+1} = a_1 + (a + b^3)[/MATH]
[MATH]a_1 = 15[/MATH][MATH]a_{2} = 15 + (1 + 1^3) = 17[/MATH][MATH]a_{6} = 15 + (9 + 5^3) = 149[/MATH]
But that's exactly the same as [MATH]a_{n+1} = 15 + (a + b^3)[/MATH], since [MATH]a_1 = 15[/MATH]!

All you're doing is saying not to apply the formula for [MATH]a_1[/MATH].
 
But that's exactly the same as [MATH]a_{n+1} = 15 + (a + b^3)[/MATH], since [MATH]a_1 = 15[/MATH]!

All you're doing is saying not to apply the formula for [MATH]a_1[/MATH].
I was just guessing that what it was meant. Since it is just a game, the author could mean anything.

And there you go with a new sequence, but I think we got some ideas how the author was thinking. It seems, this sequence will be solved easily.
 
Okay I have This number series
3,9, 24, 57,?, 267, 552.



Options:

121,118,114,126.
[MATH]3[/MATH]
[MATH](3)(2) + 3 = 9[/MATH]
[MATH](9)(2) + 3 + 3 = 24[/MATH]
[MATH](24)(2) + 3 + 3 + 3 = 57[/MATH]
[MATH](57)(2) + 3 + 3 + 3 + 3 = 126[/MATH]
[MATH](126)(2) + 3 + 3 + 3 + 3 + 3= 267[/MATH]
[MATH](267)(2) + 3 + 3 + 3 + 3 + 3 + 3= 552[/MATH]
 
Okay I have This number series
3,9, 24, 57,?, 267, 552.
Options:
121,118,114,126.
How many more are there?
126
[MATH]a_1=3, a_{n+1}=2a_n+3n[/MATH]
or

[MATH]a_n=9\times 2^{n-1} - 3(n+1)[/MATH]
 
Last edited:
[MATH]3[/MATH]
[MATH](3)(2) + 3 = 9[/MATH]
[MATH](9)(2) + 3 + 3 = 24[/MATH]
[MATH](24)(2) + 3 + 3 + 3 = 57[/MATH]
[MATH](57)(2) + 3 + 3 + 3 + 3 = 126[/MATH]
[MATH](126)(2) + 3 + 3 + 3 + 3 + 3= 267[/MATH]
[MATH](267)(2) + 3 + 3 + 3 + 3 + 3 + 3= 552[/MATH]
Okay.

I don't know how much I have to try to solve the number series by my own.

Seriously the logic didn't occurred to me for once .today I gave 12 hrs behind this sum!
 
512s - 343r
Okay.

I don't know how much I have to try to solve the number series by my own.

Seriously the logic didn't occurred to me for once .today I gave 12 hrs behind this sum!
If these problems are given on a timed test, skip them. They do not have unique correct answers. Finding even one correct answer is time consuming. Do other problems that are better worth your time.

These problems do not teach you anything.
 
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