92 Tuesday November 7Th 2017

[eiei0]

If you were given pocket money of 1p the first week, then 2p the second week, 4p the third week, 8p the fourth week and so on, doubling up each week, how long would it be before you have saved one million pounds?

My answer does not agree with that given on
http://www.bbc.co.uk/programmes/articles/3H2M2TVPvJXBygxbzT92C29/puzzle-for-today

[Tilly2]

I made it 25 weeks

[aelmpvw]

i make it 28 weeks for £1,342,177 28p

[Baldric]

I Googled the first 2 lines of the question, there are a number of Sites giving the answer as 27 wks

[Mamyalynne]

Yes, 27

https://tinyurl.com/y8rzqwxo

[elliemay1]

I get the exact same answer as ael,

[Sam1960]

If you add all your money together, by week 27 you should have
£1,342,176, 63p

[elliemay1]

Wk 28=£1,342,177.28 so it would take 27 wks

[Tilly2]

I miscalculated.

[Tilly2]

I used a calculator and kept dividing by two. I must has lost count. :-(

[Sam1960]

I did that as well Tilly, but the question is "how long before you have saved" 1 million. That was why i started adding the weekly amounts together

[Calibax]

If the money doubles every week then after n weeks you will have 2^n -1 Pence.
To get £1m
2^n -1 = 1,000,000.00
Taking logs of both sides
n log2 - log1(zero) = log 1000000000

n = log(100000000) /log(2) = 8 / 0.301 = 26.57

As it must be a whole number of weeks it takes 27 weeks