Q&A - P2 Math

[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.

[larkspur]

Need help on this question


100 sweets are divided equally among 5 girls. Each girl puts her share equally into 2 bags. How many sweets are there in each bag?

[SZ Venture]

larkspur:

Need help on this question


100 sweets are divided equally among 5 girls. Each girl puts her share equally into 2 bags. How many sweets are there in each bag?

Hi Larkspur,

#1, we will take 100 / 5 = 20 sweets each girl.

#2, 20 sweets placed into 2 bags equally, meaning 10 per bag

#3, 10 * 5 girls (since all 5 put them into the bag) = 50 sweets per bag.

[larkspur]

SZ Venture:

larkspur:

Need help on this question


100 sweets are divided equally among 5 girls. Each girl puts her share equally into 2 bags. How many sweets are there in each bag?

Hi Larkspur,

#1, we will take 100 / 5 = 20 sweets each girl.

#2, 20 sweets placed into 2 bags equally, meaning 10 per bag

#3, 10 * 5 girls (since all 5 put them into the bag) = 50 sweets per bag.

Hi SZ Venture,

the answer is 10. i also thought answer 50 but the answer is10.