Q&A - P3 Math

[Lynn2010]

Ans is 45

[Divha]

Thanks a lot PHP for your detailed solution. Easy to explain to my DS. Thanks.

[fohope]

Hi,

Pls help me to solve these problems and thanks in advance to everyone.

1) 21 handshakes were exchanged at a party. If each person only shook hand with another person once, how many people were there at the party?

2) Alex and Eugene have an equal number of marbles at first.
After Alex give Eugene 20 marbles, Eugene has twice as many marbles as Alex.
How many marbles does Alex have at first?

for question 2, can draw the model for me.

[php]

fohope:

Hi,

Pls help me to solve these problems and thanks in advance to everyone.

2) Alex and Eugene have an equal number of marbles at first.
After Alex give Eugene 20 marbles, Eugene has twice as many marbles as Alex.
How many marbles does Alex have at first?

Using Total Unchanged Concept,

Before
Alex - 1u, Eugene - 1u, Total - 2u

After
Alex - 1p, Eugene - 2p, Total - 3p

Make the total units similiar,

Before
Alex - 3p, Eugene - 3p, Total - 6p

After
Alex - 2p, Eugene - 4p, Total - 6p

1 unit = 20
3 units = 20 x 3 = 60

Ans : 60

[tianzhu]

fohope:

for question 2, can draw the model for me.

Hi

Hope this helps.

Best wishes

http://farm8.staticflickr.com/7089/7201776920_8228f273ec_z.jpg\">

[tianzhu]

fohope:

Hi,

Pls help me to solve these problems and thanks in advance to everyone.
1) 21 handshakes were exchanged at a party. If each person only shook hand with another person once, how many people were there at the party?

Hi

This question is pretty similar to yours.Try to understand the logic behind the solution and apply it to your question.

The answer to your question is 7.

Best wishes.

http://farm6.staticflickr.com/5307/5668798707_dd4d6f1925_z.jpg\">

[Cher2101]

Dear parent is there a method to answer the below question.


A) there are 16 ducks and cows on a farm altogether. The animals have 60 legs In all. How many ducks and how many cows are there on the farm?

[php]

Cher2101:

Dear parent is there a method to answer the below question.


A) there are 16 ducks and cows on a farm altogether. The animals have 60 legs In all. How many ducks and how many cows are there on the farm?

Using Chicken-Rabbit Concept,

Assume all are ducks

16 x 2 = 32 legs

60 - 32 = 28

Diff in legs --> 4 - 2 = 2

No of cows --> 28 div 2 = 14
No of ducks --> 16 - 14 = 2

For checking,

(14 x 4) + (2 x 2) = 56 + 4 = 60

[HAPPYH]

php:

Cher2101:

Dear parent is there a method to answer the below question.


A) there are 16 ducks and cows on a farm altogether. The animals have 60 legs In all. How many ducks and how many cows are there on the farm?

Using Chicken-Rabbit Concept,

Assume all are ducks

16 x 2 = 32 legs

60 - 32 = 28

Diff in legs --> 4 - 2 = 2

No of cows --> 28 div 2 = 14
No of ducks --> 16 - 14 = 2

For checking,

(14 x 4) + (2 x 2) = 56 + 4 = 60

I am aware this method for 2 variables. Can we apply this for 3 variables, say cows, ducks and one more animal say insect or 10-cent, 20-cent and 50-cent coins? Thanks in advance.

[Michaelia0816]

Not possible, to use three, but after comparing two and found one of it, use it for another to compare.