Cortana2:
You've almost nailed a job and then the interviewer placed on your table a white paper containing the following...

Legend has it that the inventor of the game called chess was told to name his own reward. His reply was along this lines.

Imagine a chess board.

Suppose one grain of corn is placed on the first square.
2 grains on the second
4 grains on the third,
8 grains on the fourth,

and so on until you get to the 64th square.

I would like as many grains of corn as the chess board now carries.

We were given just 5 minutes to do this...

use geometric progression to solve it. also apply the formula used to find the sum of the series in a geometric progression.
dont have these formulas by heart but if i do, the maths is pretty simple.

wristbangle:


Na this kind babe person go marry, e no go fear say hin children go dull. Kudos.

Geometric Progression(GP) = a ( r^(n-1))

Using the formula to solve the equation, it bcomes 2 ^ 63 as the final answer.

That is wrong,
Its sum of gp,
What u solved is juss d nth tern ie 64th term

Ifeshyne:
This is a geometric progression (g.p) with ratio = 2, a = 1 (first number) and n = 64.
we use formula for sum of a geometric progression which is s = a(1-r^n)/1-r


After substituting the values, Final answer has to be in standard form if calculators are not allowed
Something like 2^64 - 1 or even just 2^64

Ifeshyne:
This is a geometric progression (g.p) with ratio = 2, a = 1 (first number) and n = 64.
we use formula for sum of a geometric progression which is s = a(1-r^n)/1-r


After substituting the values, Final answer has to be in standard form if calculators are not allowed
Something like 2^64 - 1 or even just 2^64

Damm...na this kind wife i dey find.i love you this

tobimillar:


There is a formula for sum of terms in a gp



Ifeshyne, they asked for total number of corn, not the number of corn on the last term.

We should have used the formula for sum which is

S = a { 1- r^n/ 1-r} since r is not equal to 1

you are on point.
so many others are in a hurry to answer the question that they failed to read the question correctly.

wristbangle:


Solve (64 -1) differently, u will have 63 which is raise power of 2.

Is that what you were taught in school?

You mean 2^3-1 which is (2*2*2) - 1 = 7

is the same thing as 2^(3-1) which is 2^2 =4

Guys stop confusing yourself, it just d application of GP you learnt in school, "Ifeshyne" was in line, only she mixed-up the formula. should have been [a(r^n -1)]/(r-1) since the value of the common ratio is greater than 1 (2/1=2, or 4/2= 2) the answer to the question is 2.9*10^17 corns

Cortana2:

We were given just 5 minutes to do this...

I'm sure you didn't get the job.... and all those commenting so far would not have either.Five minutes to do what? .... what was presented to you was not to test your Maths but to test your comprehension. You were given five minutes to say how much you want to be paid... not to calculate how many grains of corn would be on the chess board. That was an indirect answer the chess inventor gave.... you could've done the same by saying the same as the pores on the interviewers body... or more appropriately... just give the salary you want.

femi4:
Is that what you were taught in school?

You mean 2^3-1 which is (2*2*2) - 1 = 7

is the same thing as 2^(3-1) which is 2^2 =4

Why are u finding it difficult it comprehend bro.

2 ^(64-1) = 2^63

Ah ahn! Na wao

refreshrate:
Me I will just stand up and say "bros if you no wan give me the job talk so na which one be all dis?" I offend you before?

wristbangle:


Why are u finding it difficult it comprehend bro.

2 ^(64-1) = 2^63

Ah ahn! Na wao

Its wrong. You even miss the formula
The formula is a(r^n - 1)/r-1 not a(r^(n-1))

this is just bollocks, how much will they now pay?? that kind company no go get money pay salary.

tobimillar:


There is a formula for sum of terms in a gp



Ifeshyne, they asked for total number of corn, not the number of corn on the last term.

We should have used the formula for sum which is

S = a { 1- r^n/ 1-r} since r is not equal to 1

Thats what i used, kindly scroll up

The simple way to do this in case of any of you do run across this again is to add the 1st and last digit i.e. 1 + 64 = 65. Then 64 divided by 2 = 32. Your answer is 65 multiplied by 32 = 2080.

I like this question. There are certain pitfalls however. How many grains are on the board?
1, 2, 3, 4, ..........
on the 64th square you would have 2 power 63 as many people have pointed out. But the real question is how many is on the board?
So you have to sum from the 0 to 63 using the geometric sum
(2 power (63 +1)) - 1

The minus one is not on the power, else you would only computing the number on the 64th square

H2Ossss:


U go school.... This is simply application of what u learnt in school in a real life situation.

What if you don't remember the formula at that time? That is just the issue

pinkyruledworld:
I dont even understand

hahahahah

femi4:
haba, how can 2^64 - 1 = 2^63

I tell you, the minus 1 is not for the 64 only but for 2^64

do u want to give me d job or not

Ifeshyne:


I tell you, the minus 1 is not for the 64 only but for 2^64

I don correct am taya....e no gree

Cc wristbangle

agrovick:


Let me break it down a bit, 2 is the common factor (don't ask me how, I only took an informed guess)
1st square = 2^1-1 = 2^0 = 1
2nd square= 2^2-1 = 2^1 = 2
3rd square = 2^3-1 = 2^2 = 4
4th square = 2^4-1 = 2^3 = 8
64th = 2^64-1 = 2^63

bro, that is 64th term alone.. The question is the sum of everything on the chess board which will be the sum of all the 64 terms..

I still insist that the answer is 2⁶⁴ - 1

Zirah:
There's nothing wrong about it. 2 to the power of 63 is correct and you don't need any formula to get this solved

you definitely need a formula.. This is a GP series of the form 1, 2, 4, 8, 16, 32,...

From the above,
first term, a = 1, common ratio, r = 2,
supply this in the formula of sum of nth term of a GP..
S_n = a(rⁿ - 1)/(r-1) since r > 1

therefore, S₆₄ = 1(2⁶⁴ - 1)/(2-1),
S₆₄ = 2⁶⁴ - 1

obstead200:
you are on point.
so many others are in a hurry to answer the question that they failed to read the question correctly.

And you're in a hurry to comment and didn't read the answer correctly

Ifeshyne:


Thats what i used, kindly scroll up

I didn't see that earlier. My bad. My response then is to those asking if we were still going to add from first to last term.how did you arrive at 2^63 as your final answer. That looks like the last term to me. And your formula wasn't complete. Look at yours and compare with mine

MsFaith:


What if you don't remember the formula at that time? That is just the issue

Yeaa... U are right... But at least the 1st step is knowing what to do... Some might know the formula without knowing to apply it in a given situation.

Emary:
The simple way to do this in case of any of you do run across this again is to add the 1st and last digit i.e. 1 + 64 = 65. Then 64 divided by 2 = 32. Your answer is 65 multiplied by 32 = 2080.

Wrong
Answer is uncountable

femi4:
Its wrong. You even miss the formula
The formula is a(r^n - 1) not a(r^(n-1))

Google the formula sir.

wristbangle:


Google the formula sir.

you still dey argue

Nth term formula is different from Summation formula

You ve been using nth term formula which is wrong

Wats funny is that this job will not entail what the stupid interviewer is asking you to calculate.

Interviewer sef.

smh

LastMumu:
What's with the whole interest in corns and grains? If I were you, I would have asked the recruiter if he was a fowl in his previous life.


lastmumu

oh boy I beg,you don make me look stupid where I dey,in the mix of some chicks...niga blow serious laugh...

dejt4u:

bro, that is 64th term alone.. The question is the sum of everything on the chess board which will be the sum of all the 64 terms..
I still insist that the answer is 2^64

You might be correct, I realized all I did was look for the 64th term, I didn't do the summation.

tobimillar:

It's only for when r > 1. When r =1 or less than 1, there is a different formula

I agree, r > 1 applies here. Although I was trying to get you to remind me of the conditions that r fulfills before one can decide the formula to be used.

Originalsly has a point with his post.

Filashade:
Wats funny is that this job will not entail what the stupid interviewer is asking you to calculate.

Interviewer sef.

smh

Not really, the job might require you to use simple maths/physics principles to solve complex problems... I'll love to believe its for an engineering role..

Ifeshyne:
This is a geometric progression (g.p) with ratio = 2, a = 1 (first number) and n = 64.
we use formula for sum of a geometric progression which is s = a(1-r^n)/1-r


After substituting the values, Final answer has to be in standard form if calculators are not allowed
Something like 2^64 - 1 or even just 2^64

To you madam,I say 'well done'



And for the records(as pathetic as it may sound), I hate Mathematics.

Ohkay, nor be say i hate maths...I nor just gree know am. I pray to give birth to children,in future who are mathematics geniuses.

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