Q&A - P2 Math

[numeric]

A duck has 2 legs, and a cow has 4 legs.

There are 38/2 = 19 pairs of legs.

So i will just assign 2 pairs of legs to a cow, 1 pair of legs to a duck. This pattern repeats until I hit 12 animals.
The last 2 pairs of legs has to be for a cow, not for 2 ducks. Otherwise you won't get 12 animals.

http://i49.tinypic.com/fctton.jpg\">

[numeric]

fable:

sembgal:

[quote=\"dolphin\"]Hi


Anyone know if there's another way to solve the below question apart from finding the combination numbers to make 14?

http://i50.tinypic.com/2gy0oxx.jpg\">

Since 7 and 8 are given,
14-8=6
14-7=7
7+6+1=14
1+5+8=14
8+2+4=14
7+3+4=14

Your patten should be

7 3 4


6 2


1 5 8

My \"lazy\" way would be to first note that 6 cannot be in either of the corner circles or next to 8 as it would total 14. So I'd put 6 next to 7 (either across or down, doesn't matter), so 1 would go into the corner circle next to that, and 5 goes between 1 and 8. That leaves 2, 3 and 4, so 4 would have to go in the other corner circle, leaving 3 between 7 and 4, and 2 between 8 and 4.[/quote]
Heuristics: Yep. 6 cannot be at the corner or at the right side (they will add up to 14 just with 2 numnbers).
So let's put 6 at the top middle circle.
It means the top corner is 14-7-6=1.
So the right side circle is 14-8-1=5.

We are now left with 2, 3, 4.
The left circle and bottom corner circle adds up to 7. So we use 3 for left circle and 4 for bottom corner circle.
This leaves 2 for the bottom middle circle.

[maltbibi]

jolenekoh:

Please help... How to draw model for this question or table method?


There is a total of 12 cows and ducks on a farm. They have 38 legs altogether. How many cows are there on the farm?

Appreciated

Hi.

Can we solve this using model?

Thanks.

[sembgal]

maltbibi:

jolenekoh:

Please help... How to draw model for this question or table method?


There is a total of 12 cows and ducks on a farm. They have 38 legs altogether. How many cows are there on the farm?

Appreciated

Hi.

Can we solve this using model?

Thanks.

Can only use Guess and Check method. Draw Guess and Check table to solve.
Answer: 7 cows , 5 ducks.
Tip: Average the animals. Take 12/2 = 6
Try 6 cows, 6 ducks first.
6 cows x 4 legs = 24 cows' legs
6 ducks x 2 legs = 12 ducks' legs
Total legs: 24 + 12 = 36 legs (wrong) x

Try again: this time to increase number of legs, presume 1 more cow and 1 less duck.

Now try 7 cows, 5 ducks
7 cows x 4 legs = 28 cows' legs
5 ducks x 2 legs = 10 ducks' legs
Total legs: 28 + 10 = 38 legs (correct)

Final answer: 7 cows

[maltbibi]

Thanks Sembgal

[gal711]

Qns: Mr Tan was selecting children to perform in a concert. 100 children were given numbers 1 to 100. He picked the child ugh the number 3. He then skip-counted in tens to pick the other children. Write down the numbers of the other children who were selected.


I was think if the answer is 13,23,33,43,53,63,73,83,93. I don’t understand what they mean by skip-counted in tens.

Experienced parents, please help me. Thks

[JLxu70]

sembgal:

maltbibi:

[quote=\"jolenekoh\"]Please help... How to draw model for this question or table method?


There is a total of 12 cows and ducks on a farm. They have 38 legs altogether. How many cows are there on the farm?

Appreciated

Hi.

Can we solve this using model?

Thanks.

Can only use Guess and Check method. Draw Guess and Check table to solve.
Answer: 7 cows , 5 ducks.
Tip: Average the animals. Take 12/2 = 6
Try 6 cows, 6 ducks first.
6 cows x 4 legs = 24 cows' legs
6 ducks x 2 legs = 12 ducks' legs
Total legs: 24 + 12 = 36 legs (wrong) x

Try again: this time to increase number of legs, presume 1 more cow and 1 less duck.

Now try 7 cows, 5 ducks
7 cows x 4 legs = 28 cows' legs
5 ducks x 2 legs = 10 ducks' legs
Total legs: 28 + 10 = 38 legs (correct)

Final answer: 7 cows[/quote]Another way that I read from my son's Math Olympia book, also called chicken and rabbit problem.

Step 1 - Assume they are same animals with the smallest number of legs. In this case, assume they are all ducks.
Step 2 - with all being ducks, total number of legs are: 12X2=24
Step 3 - there are 38-24=14 extra legs.
Step 4 - The difference of legs between cow and duck is: 4-2=2
Step 5 - use the result from step 3 and 4: 14/2 = 7, so there are 7 cows.
Step 6 - 12-7=5, there are 5 ducks.

To verify the result, 7X4+5X2=38 legs.

[PapayaDad]

gal711:

Qns: Mr Tan was selecting children to perform in a concert. 100 children were given numbers 1 to 100. He picked the child ugh the number 3. He then skip-counted in tens to pick the other children. Write down the numbers of the other children who were selected.


I was think if the answer is 13,23,33,43,53,63,73,83,93. I don't understand what they mean by skip-counted in tens.

Experienced parents, please help me. Thks

You are correct. Also I found this.. hope it helps :

http://www.mathsisfun.com/numbers/skip-counting.html

[jenao]

HI all,


For multiplication and division, does it matter eg 5x4=20 or 4x5=20 or 20 /4=5 or 20/5=4? Or it must be strictly a group of b is axb and not bxa?

Appreciate comments. Thanks.

[nicnac]

5 x 4 should read 5 groups of four… Whereas 4 x 5 should read 4 groups of 5. Different meaning. I guess this is only important when they are only beginning to learn multiplications… Easy for them to grasp the concept by simply replacing the ‘group of’ with the x sign. Similarly with the division.