Q&A - P3 Math

[tianzhu]

Dharma:

Thanks Tianzhu.

Hi Dharma

You are welcome.
Enjoy your reading.

Best wishes

[Suz855]

A book has 110 pages. How many times does the digit 8 appear as a page number?


Qn : should page 88 counted as 2 8s or just 1?

Thanks for the clarification & help

[Daddy]

Hi,


I have a question to ask. Thanks.

\"When Sean bought 8 pens, he was short of $38. When he bought 10 pens, he was short of $110. How much money did he have?\"


Daddy :?

[Dharma]

Suz855:

A book has 110 pages. How many times does the digit 8 appear as a page number?


Qn : should page 88 counted as 2 8s or just 1?

Thanks for the clarification & help

Hi Suz855,

On page 88, the digit ‘8’appears twice.

However, if the qns goes like this .. How many pages numbers contain a digit ‘8’?
Then you take page 88 containing digit 8. Page 88 is one of the pages that contain the digit ‘8’.

[Dharma]

Daddy:

Hi,


I have a question to ask. Thanks.

\"When Sean bought 8 pens, he was short of $38. When he bought 10 pens, he was short of $110. How much money did he have?\"


Daddy :?

Hi Daddy,

If Sean bought 2 extra pens, he spent an additional ($110 - $38 ) = $72.
Cost of 1 pen = $72/2 = $36

Amount of money Sean had = ($36 x 10) - $110 = $250

Or

Amount of money Sean had = ($36 x 8 ) - $38 = $250

[BigDevil]

Daddy:

Hi,


I have a question to ask. Thanks.

\"When Sean bought 8 pens, he was short of $38. When he bought 10 pens, he was short of $110. How much money did he have?\"


Daddy :?

My first crack at using model...got to get myself ready to help my DD in the future...

Can the maths guru comment whether I'm doing it correctly?


http://www.postimage.org/image.php?v=gxmx2PA

[elkniwt]

Suz855:

A book has 110 pages. How many times does the digit 8 appear as a page number?


Qn : should page 88 counted as 2 8s or just 1?

Thanks for the clarification & help

88 should be counted as 2.
For (1-10), (11-20),...(61-70), - for each set, digit 8 appears once -> 1x7
For (71-80) -> digit 8 appears twice (78 and 80) -> 2
For (81-90) -> digit 8 appears 10 times since 88 is counted twice
For (91-100) (101-110) - each set once -> 2
Total = 21

[BigDevil]

ameryeducation:

BigDevil:

My first crack at using model...got to get myself ready to help my DD in the future...


Can the maths guru comment whether I'm doing it correctly?


http://www.postimage.org/image.php?v=gxmx2PA

Your model, method and answer are all correct and clear.

A tip for a possible improvement in the way to draw the model would be to place the 8 blocks directly on top of the 10 blocks, and then putting a vertical line cutting both the 8 blocks and the 10 blocks in one stroke at an arbitrary point and shading the left side. The right side can then be labelled with $38 for the top, and $110 for the bottom. This might help your child to visualise the problem better.

Thanks! Those are wonderful tips!
Will try again when there's another question posted.

[Daddy]

Hi Dharma,


I had came across this question. But the two conditions are different. Ones is short & the other is left. Add two together..

e.g: Sally bought 7 rings, she was short of $192. When she bought 5 rings, she had $88 left.

I just added the two value: $192+$88 = $280, then $280/2 = $140.

But came to this question: Both conditions are same. ???
\"When Sean bought 8 pens, he was short of $38. When he bought 10 pens, he was short of $110. How much money did he have?

How about if two conditions are left(remainder) of money. subract the 2 remainder.???

Any easy method to understand?...

Thanks alot...

Daddy

[Dharma]

Daddy:

Hi Dharma,


I had came across this question. But the two conditions are different. Ones is short & the other is left. Add two together..

e.g: Sally bought 7 rings, she was short of $192. When she bought 5 rings, she had $88 left.

I just added the two value: $192+$88 = $280, then $280/2 = $140.

But came to this question: Both conditions are same. ???
\"When Sean bought 8 pens, he was short of $38. When he bought 10 pens, he was short of $110. How much money did he have?

How about if two conditions are left(remainder) of money. subract the 2 remainder.???

Any easy method to understand?...

Thanks alot...

Daddy

Hi Daddy,

Just remember this … “short of $x” means one needs $x more than the amount he already has to buy certain number of items while “had $xx left” means the excess/balance amount he has after buying certain number of items.

For 1st example

Sally bought 7 rings, she was short of $192. When she bought 5 rings, she had $88 left.

So, if Sally buys 2 (7-2) less rings; the extra amount of money she saves is $ 88 + $192 = $280.

This $280 is actually the cost of the 2 rings … Therefore, 1 ring will cost him $140.

In the 2nd example
\"When Sean bought 8 pens, he was short of $38. When he bought 10 pens, he was short of $110. How much money did he have?

Buying 2 extra pens will cost Sean $ 110 - $38 = $72 … Cost of each pen = $36
Amt of money he had = ($36 x 10) - $ 110 = $250

I hope you are able to understand the difference between the 2 examples above. Please not get your child to just memorize the rule (to add or subtract based on the conditions), but rather try to get him to appreciate what the question is asking.