Math Is Fun Forum

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: Oral puzzles

hi ganesh

Last edited by anonimnystefy (2011-06-08 05:58:46)

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“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: Oral puzzles

hi bobbym

i think that you missed the minus sign instead of plus.

---

“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Oral puzzles

Hi anonimnystefy;

I think you are right my answer was kaboobly doo. I fixed it and advised ganesh of the correction.

Hi ganesh;

Sorry for the confusion. Check anonimnystefy's answer and we can continue.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

reconsideryouranswer

Member

Registered: 2011-05-11

Posts: 171

Re: Oral puzzles

Hi bobbym,

The solution 1048 is perfect. Good work!

#1049. Find the sum to n terms of the series

.

bobbym and anonimnystefy,

for #1049, neither of your answers *were* correct. 

Notice if n = 1 in your formulas, neither produces 2/3, which is the 1st term of the series.

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bobbym,

Then, the summation on the right-hand side of the subtraction sign is equal to:

The whole infinite series (**) sums to 1/2.

Edit:
------

I will take the credit for the solution.

Last edited by reconsideryouranswer (2011-06-08 08:41:33)

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Signature line:

I wish a had a more interesting signature line.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Oral puzzles

Hi;

Yes, I know, it has already been straightened out. Check the earlier posts to yours. I edited my answer. It now generates the sum. Just a latex error.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

reconsideryouranswer

Member

Registered: 2011-05-11

Posts: 171

Re: Oral puzzles

These questions are to be attempted to be answered orally,
and attempted within a minute, without the use of paper, pen/pencil and calculator.

After sampling many questions here,  I would propose the above alteration to be realistic.  And my
involvement/effort to my solution to #1049 would be representative of that change.

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Edit:
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_______________________________________________________________________
ashwil
    Full Member

Re: Oral puzzles

mathsy, 2 easy ways of getting approximate answers to 20 without a calculator:-

a) every power of 10 requires just over 3 powers of 2. Therefore 50 powers of 2
suggests between 15 and 16 powers of 10.
b) If you know that log 2 = 0.3010 (which you should!), then log 2^50 = 15.05.
Again, about 15 powers of 10

By both methods, this gives me 16 digits in the answer.

_______________________________________________________________________

But how would a person know that they would be correct with either of those methods?

Last edited by reconsideryouranswer (2011-06-08 09:16:44)

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Signature line:

I wish a had a more interesting signature line.

Jai Ganesh

Administrator

Registered: 2005-06-28

Posts: 46,755

Re: Oral puzzles

Hi reconsideryouranswer,  anonimnystefy, and bobbym,

The solution 1049 given by  reconsideryouranswer is perfect. Excellent!

I carry on with the puzzles.

#1050.   If

, find the value of x.

---

It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Oral puzzles

Hi ganesh;

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Jai Ganesh

Administrator

Registered: 2005-06-28

Posts: 46,755

Re: Oral puzzles

Hi  bobbym,

The solution given 1050 is perfect. Excellent performance!

#1051.

---

It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Oral puzzles

Hi;

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Jai Ganesh

Administrator

Registered: 2005-06-28

Posts: 46,755

Re: Oral puzzles

Hi bobbym,

The solution 1051 is in order. Good work!

#1052. If

, then what is the value of a and b?

---

It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Oral puzzles

Hi;

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: Oral puzzles

hi ganesh

---

“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

Jai Ganesh

Administrator

Registered: 2005-06-28

Posts: 46,755

Re: Oral puzzles

Hi bobbym and anonimnystefy,

The solution 1052 is perfect. Excellent!

#1053.

---

It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Oral puzzles

Hi ganesh;

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Jai Ganesh

Administrator

Registered: 2005-06-28

Posts: 46,755

Re: Oral puzzles

Hi bobbym,

The solution 1053 is perfect. Brilliant work!

#1054.

---

It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Oral puzzles

Hi ganesh;

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: Oral puzzles

hi ganesh

---

“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

Jai Ganesh

Administrator

Registered: 2005-06-28

Posts: 46,755

Re: Oral puzzles

Hi bobbym and anonimnystefy,

The solution 1054 is correct. Remarkable!

#1055.

---

It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Oral puzzles

Hi;

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Jai Ganesh

Administrator

Registered: 2005-06-28

Posts: 46,755

Re: Oral puzzles

Hi bobbym,

The solution 1055 is correct. Neat job!

#1056.

---

It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Oral puzzles

Hi;

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Jai Ganesh

Administrator

Registered: 2005-06-28

Posts: 46,755

Re: Oral puzzles

Hi bobbym,

The solution 1056 is correct. Neat job!

#1057.

---

It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Oral puzzles

Hi ganesh;

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Jai Ganesh

Administrator

Registered: 2005-06-28

Posts: 46,755

Re: Oral puzzles

Hi bobbym,

The solution 1057 is perfect. Neat job!

#1058. If

, then what would be the value of

?

---

It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.