10

1
Tue 9 Mar, 2010 12:48 am
@georgeob1,
georgeob1 wrote:

On reflection, I prefer Aidan's as well.

Mine is second best.

i'm no mathematical genius either.
Why would it ever cross anyones mind (never mind an 8 year old) to use the square root function george?

Dorothy the problem is all about using the clues provided, (answer ends in 5 so must be a number ending with 5) narrowing the options (see francic's post) then "guess and check"
0 Replies

aidan

2
Tue 9 Mar, 2010 01:46 am
@Dorothy Parker,
Quote:
Unfortunately, I am unable to explain the working out of this maths problem. Even if I were to re-read it a hundred times, I would still not understand it.

Part of the problem might be that you're unfamiliar with the terminology- which would be true of a lot of people who aren't currently taking math - it's amazing what'll come back to you when you go through a math book.

The multipliers are the numbers you are multiplying together to find the answer (which is called a product when it's found by multiplying). So 63 and 65 are your multipliers. 4095 is your product. 4095 is a multiple of 5 - you know that because it ends in 5. When someone says something is a multiple of 5 that means that the number 5 can be divided into it evenly with no remainder. Just like 100 is a multiple of 10 because ten can be divided into 100 evenly.
Any number that ends in 5 or 0 is a multiple of 5 (if you count by fives you will say all the multiples of 5).
When a number ends in 5 - we know for sure that another number that ends in 5 has to be one of the multipliers (as long as we're talking about whole numbers). So in this problem, that tells you that one of the multipliers is either 55 or 65 because those are the only two whole numbers between 50 and 70 that end in 5 (or that have a 5 in the ones place).
At this point I rounded off 4095 to 4000 in my head and I said to myself - even if I multiply 55 by 70 (even though I knew that wouldn't give me 4095 because I'd have a 0 in the ones place instead of a 5) that would only get me 3850 - less than 4000- so the only other choice of a multiplier that ends in 5 is 65 and once you have that it's very simple and fast to divide the product they gave you (4095) by 65 and get the other multiplier (63).

Quote:
It used to reduce me to tears at school cos I just could not get my head round certain things.

I felt the same way about science after biology. I got biology - but I just couldn't get chemistry and I struggled through that and then gave up on science- concentrating on math and english -which I liked. That was fine on one level, but sad on another because I really did think there was something wrong with my brain and I couldn't learn science.

But then when I was an adult and teaching I used to sit in the highschool science classes and I was amazed at how much better I was at comprehending the text, the teacher, etc.
Maybe because the pressure was off - maybe my concentration was better and more focused on the information instead of all the other stuff I found to think about when I was actually in highschool - I don't know...I know it wasn't the information that had changed so it had to be something about me.

Quote:
God knows how I will help her with the maths homework when she's at high school.

Do whatever she's doing with her now as she's doing it. I don't mean do it FOR her, but have your own paper and do it as she's doing it. Having her explain to you whatever she learned in class that day will reinforce the lesson in her mind which can only help her and you sitting there with her will force you to learn step by step (which is how you have to learn math) what either you didn't ever learn in the first place or have forgotten.
This is a good spot to start. Once she gets into fractions, decimals, percents, etc...and onto geometry and algebra - if you haven't got the foundation down- numeration, multiples, factoring, etc.- it'll be much harder to just jump in and automatically recollect all the stuff you've forgotten.

Good luck!

McTag

1
Tue 9 Mar, 2010 02:41 am

I liked aidan's first answer best.
aidan

1
Tue 9 Mar, 2010 03:10 am
@McTag,
I was just trying to encourage her in terms of not feeling inadequate helping a kid with math homework. It's hard to remember all that stuff if you haven't done it in a while. It doesn't mean she can't be good at it if she takes a little refresher course.

My second answer is better in terms of that.
0 Replies

engineer

1
Tue 9 Mar, 2010 07:28 am
@McTag,
McTag wrote:

Quote:
Well, you know that at least one of the multipliers has to have a 5 in the one's place because your product is a multiple of 5. So one of your multipliers has to be either 55 or 65 because those are the only two whole numbers that fit the criteria between 50 and 70. So I divided 4095 by 65 and got 63.

65x63= 4095

As did I. This type of problem is always going to have some trial and error to it. The trick is to reduce the trials to something you can go through quickly or to find a trial that is much more likely than the other possibilities. Aiden's answer latched on to the key clue of ending in 5 and went from there. If I were advising a child on how to do this problem in general, I would say "look for the clues like that last digit."
0 Replies

Dorothy Parker

1
Tue 9 Mar, 2010 01:17 pm
@aidan,
Thank you aidan. What you say makes sense and I know I should not just "do it for her" as this doesn't help her learn . I think it doesn't help that I work things out in a different (and probably clumsy) way and to try and explain to her how I arrived at an answer is hard, especially when I can see her losing interest after 30 seconds. :-)
0 Replies

amy youd xx

1
Sat 26 Feb, 2011 10:15 am
@Dorothy Parker,
63 and 65 are the number if anyone is stuck on the puzzle this is it

0 Replies

georgeob1

1
Thu 3 Mar, 2011 11:08 pm
@Francis,
OK, I've thought about it some more. The prime factors of 4095 are 13, 7, 3, 3, and 5. Thus 13x7x3x3x5 = 4095. Now look for product combinations between 50 and 70. 7x3x3 = 63, and 13x5 = 65. Voila !
0 Replies

raprap

1
Thu 3 Mar, 2011 11:36 pm
@Dorothy Parker,
4095= 3*3*5*7*13 5#13=65 3*3*7=63

check Sqrt(4095)=63.922... the two whole #'s are close to the square root of 4095 65 & 63 are close.
0 Replies

kpinky

0
Sun 15 Apr, 2012 07:21 pm
Hey I have some query Explain why 7 × 11 × 13 + 13 and 7 × 6 × 5 × 4 × 3 × 2 × 1 + 5 are composite numbers do you have any easier method to solve this problem other than this Edit [Moderator]: Link removed If you have any easier method to solve kindly post here
markr

1
Sun 15 Apr, 2012 07:27 pm
@kpinky,
Adding two multiples of 13 yields a multiple of 13, and since the sum doesn't equal 13, it is composite (13 is the only multiple of 13 that is prime). Or you can rewrite it as (7 x 11 + 1) x 13.

Substitute 5 for 13 to get the answer to the second one.

Your other post says you are a math tutor. Shouldn't you know this?
0 Replies

raprap

1
Sun 15 Apr, 2012 07:53 pm
@kpinky,
7x11x13+13=(7x11+1)x13 =78*13=2*3*13*13 ----product of prime #

7x6x5x4x3x2x1+5=(7x6x4x3x2x1+1)x5=1oo9x5 -----product of prime #

Rap

0 Replies

raprap

1
Mon 16 Apr, 2012 05:16 am
@Dorothy Parker,
4095=3x3x5x7x13

3x3x7=63 5x13=65
3x13=39 <40 no
7x13=91>70 no
3x7=21 <40 no

so 63 and 65

Rap
Dorothy Parker

1
Fri 11 May, 2012 02:17 pm
@raprap,
This reminds me of that TV show the Big Bang Theory. I like that show, it's funny.
0 Replies

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