Help w/word problem please~thanks soo much!

[lilonepaula]

Every 5 days Alma rides her skateboard in the park. Every 4 days she bikes to her best friends house. How often does Alma do both?

Signed,
NmbrsRlkngAlk!

 

[stapel]

Find the smallest number that multiples of five and multiples of four can fit in to. Draw a grid with this many boxes, one box for each day. Start your count right after a day when she boards and bikes, so you're starting "fresh". Then:

On which days, during this time period, will she board? On which days will she bike? (Just mark the boxes.) Now go back and count the number of boxes containing two marks.

Eliz.

 

[lilonepaula]

Thank you...
I do think I am more confused now than before though,lol.
Things sure have changed since I went to school.
The kids learn math a different way too.
GD said that it is to be put into a problem..
I guess like X-Z=
?

1 is the smallest number...so 5 days of boarding and 4 days of biking=9 days total? That would be waaaay too simple so I know that can't be what they are asking..basic math.
The thing that gets me too is that it doesnt say how many days does she do both...within a week...a month...a year? Im soo lost!

 

[Denis]

Does this "ring" a bell ; S = Skateboard, B = Bike :

S 1 2 3  4 (5) 6 7 8 9 (10) 11 12 13 14 (15) 16  17 18 19 (20)
B 1 2 3 (4) 5 6 7 (8) 9 10 11 (12) 13 14 15 (16) 17 18 19 (20)

 

[stapel]

1 is the smallest number...

Really? How many times does five fit into one? How many times does four fit in?

The thing that gets me too is that it doesnt say how many days does she do both...within a week...a month...a year?

That was the point of the grid I explained (and Denis draw): you can read the answer right off the picture, as a fraction of the total time involved.

Eliz.

 

[lilonepaula]

Does this "ring" a bell ; S = Skateboard, B = Bike :

S 1 2 3  4 (5) 6 7 8 9 (10) 11 12 13 14 (15) 16  17 18 19 (20)
B 1 2 3 (4) 5 6 7 (8) 9 10 11 (12) 13 14 15 (16) 17 18 19 (20)

Thank you soo much!
I was thinking of it completely wrong (as you and others know) where as what number goes into both 4 and 5...another words like 2 can go into 4 twice but it can't evenly go into 5...so I thought 1 is the only thing that can go into both numbers instead of multiplying and getting the...common demominator is it? As you can see I am not good at math at all.Actually,I loathe it! Makes it quite hard to help a grandchild.
Thank you again for the great explaination/formula!
Now,with that info. I can help her work out other problems like it.

 

[Denis]

...so I thought 1 is the only thing that can go into both numbers instead of multiplying and getting the...common demominator is it?

It's known as the LCM (Lowest Common Multiple);
in other words, the lowest number divisible by each of the variables;
so in your case, 20, the lowest divisible by 4 and 5.

 

[lilonepaula]

Ok,I think I got it.
I definitely understand LCM now that you reminded me of what I learned years ago. But looking at the grid 20 is the LCM but reading the question "How often does Alma do both?" then the answer is 1? She rides both her S and B on the 20th day..only 1 day does she ride both...or is the answer 9 by counting the boxes? Every 5th and every 4th day up until the 20th day is 9.
So just when I think I've got it I have more questions,lol.
My GD and myself were working on adding/sub and mult/divide intergers and she had a good understanding of it (and so did I most times) but this one did not ring a bell to her at all. TY!

 

[stapel]

Every twenty days, the cycle repeats (no pun intended). During that period, how often does she bike and board on the same day?

Now form the fraction (day she does both)/(total days in period). This tells you the fraction of "all the time" during which she bikes and boards on the same day. You could also convert the answer to percentage form, if you liked. But it would not be correct to say "she bikes and boards on the same day exactly once", unless the question had specified "how often in a twenty-day period".

Eliz.

 

[Denis]

Ok,I think I got it.
I definitely understand LCM now that you reminded me of what I learned years ago. But looking at the grid 20 is the LCM but reading the question "How often does Alma do both?" then the answer is 1? She rides both her S and B on the 20th day..only 1 day does she ride both...or is the answer 9 by counting the boxes? Every 5th and every 4th day up until the 20th day is 9.
So just when I think I've got it I have more questions,lol.
My GD and myself were working on adding/sub and mult/divide intergers and she had a good understanding of it (and so did I most times) but this one did not ring a bell to her at all. TY!

Ahhh...I see where you're confused...
the skateboarding starts in 5 days (every 5th day), and for that day only;
the biking starts in 4 days (every 4th day), and for that day only;

Nothing is done in 1st 3 days; N = No skating or biking:

N N N N S N N N N S N N N N S N N N N S
N N N B N N N B N N N B N N N B N N N B

ding dong ?

 

[lilonepaula]

Thanks for replying!
Well,even though she turned it in a few days ago I wanted to post what I think is the answer:9
Sure,hope thats right but don't know how it would done as a math problem.
Would it be as simple as 4+5=9 days that she does both...out of 20?
I know you are making it clear as day but if not put into a problem with answer I don't think I will fully get it.
Its funny...the paper is turned in and done with but I am still curious.

 

[stapel]

I think...the answer [is] 9

Why? Denis has shown you that she does both only one day in twenty. Where is "nine" coming from?

Eliz.

 

[lilonepaula]

Does this "ring" a bell ; S = Skateboard, B = Bike :

S 1 2 3  4 (5) 6 7 8 9 (10) 11 12 13 14 (15) 16  17 18 19 (20)
B 1 2 3 (4) 5 6 7 (8) 9 10 11 (12) 13 14 15 (16) 17 18 19 (20)

Counting the ones in () came to 9. That's where it came from. Sorry I do not know math...and as I said earier loathe it. At least I am trying to learn it and was hoping for a formula with the answer...which is 20 now...in it. So 5x4=20 is it? Excuse me if my questions are annoying as I DONT get it and have no problem admitting this instead of saying thanks and moving on with no clue as to what or how the answer came about....
Thank you for your help Denis and for your kindness about it.

 

[Denis]

Does this "ring" a bell ; S = Skateboard, B = Bike :

S 1 2 3  4 (5) 6 7 8 9 (10) 11 12 13 14 (15) 16  17 18 19 (20)
B 1 2 3 (4) 5 6 7 (8) 9 10 11 (12) 13 14 15 (16) 17 18 19 (20)

Counting the ones in () came to 9. That's where it came from. Sorry I do not know math...and as I said earier loathe it. At least I am trying to learn it and was hoping for a formula with the answer...which is 20 now...in it. So 5x4=20 is it? Excuse me if my questions are annoying as I DONT get it and have no problem admitting this instead of saying thanks and moving on with no clue as to what or how the answer came about....
Thank you for your help Denis and for your kindness about it.

Yes: used Skateboard on day#5, day#10, day#15 and day#20: 4 times
And used Bike on day#4, day#8, day#12, day#16 and day#20: 5 times
That's a total of 9 times.

BUT BUT...it is ONLY on day#20 that both were used, right? :wink: