Math Is Fun Forum

Nasir Hassan

Member

Registered: 2020-04-11

Posts: 6

9-Digit Number Puzzle

Your solution is 473816952.  However, the question states that rounding is done alternatively - up, down, up ....  With 2 as the units digit, the 1st rounding will be down, not up.

My solution is 536192748. It's divisible by 6 and 7, and the alternative rounding starting from up then down etc  gives 53619 0000, with digits adding up to24.  Where's the flaw in this answer?  Unless the number 4 becomes 5 after the 1st round up, and the number 7 does't round down to 7 because of the 5?

Regards

Nasir

Bob

Administrator

Registered: 2010-06-20

Posts: 10,626

Re: 9-Digit Number Puzzle

hi Nasir Hassan

Welcome to the forum.

I agree that your solution is better.  The one given would be ok if the question read "it rounds in an alternate pattern (down, up, down ...).  I don't have any editorial control over the MIF site so I'll message the boss and suggest a re-write.

Best wishes, stay safe,

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

MathsIsFun

Administrator

Registered: 2005-01-21

Posts: 7,713

Re: 9-Digit Number Puzzle

Your solution is right Nasir, thank you!

And Bob is right, the old solution (473816952) works when the rounding starts at down, then up, etc

Will amend.

---

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

MathsIsFun

Administrator

Registered: 2005-01-21

Posts: 7,713

Re: 9-Digit Number Puzzle

Here is the amended puzzle:

https://www.mathsisfun.com/puzzles/9-digit-number-solution.html

Please check!

---

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman