Q&A - P3 Math

[GreenQ]

Great! Thanks for your prompt reply... :love: :thankyou:

[Maths Olympiad Tutor]

quekcc:

GreenQ:

Sorry dear parents, need solution for the question below.


Draw diagrams / Guess and Check.

There are 8 goats and ducks altogether.
Some had 2 legs and some had 4 legs.
The animals have 20 legs in all.
How many goats are there?

Thanks.

P/s: The sch teacher said to get as less as possible for the number of goats.

Draw diagram.

http://i46.tinypic.com/2njysuq.png\">

When we assume there are 8 goats, there will be 32 legs, 12 more than what is mentioned.

A goat has 2 more legs than a duck.

Since there are 12 extra legs, there must be 12 / 2 = 6 ducks.

8 - 6 = 2 goats.

[mother777]

Ok here goes my method…


There are 8 goats and ducks altogether.
Some had 2 legs and some had 4 legs.
The animals have 20 legs in all.
How many goats are there?

Answer…
Assume all are ducks…
each duck–>2 legs
If 8 ducks, total legs–>8 x 2 = 16
balance legs–>20-16 = 4
these extra legs are from goats.
each goat 2 extra leg.
so number of goat–>4/2 = 2

Goat–>2
duck–>8-2 = 6…

[GreenQ]

Thanks and appreciate all for yours replies! :thankyou:

[GreenQ]

mother777:

Ok here goes my method..


There are 8 goats and ducks altogether.
Some had 2 legs and some had 4 legs.
The animals have 20 legs in all.
How many goats are there?

Answer..
Assume all are ducks..
each duck-->2 legs
If 8 ducks, total legs-->8 x 2 = 16
balance legs-->20-16 = 4
these extra legs are from goats.
each goat 2 extra leg.
so number of goat-->4/2 = 2

Goat-->2
duck-->8-2 = 6..

Thanks mother777. My child's teacher used exactly the same method as yours!

[mother777]

well that is good to know

the best thing about this method is that guessing is eliminated.

so once you get answer and your working is correct..then you can be sure that your answer is correct only..

[tracywham]

hello, i need help on this question (with model drawing will be greatly appreciated):


Siti had 6 times as many apples as David at first. After Siti had given 450 apples to David, they had an equal number of apples.

a) Find the number of apples David have at first.

b) David gave away some apples and had half the number of apples
Siti had. How many apples did David give away?

[jieheng]

tracywham:

hello, i need help on this question (with model drawing will be greatly appreciated):


Siti had 6 times as many apples as David at first. After Siti had given 450 apples to David, they had an equal number of apples.

a) Find the number of apples David have at first.

b) David gave away some apples and had half the number of apples
Siti had. How many apples did David give away?

At first
S [2u][2u][2u][2u][2u][2u] --> (12u)
D [2u]

After Siti had given 450 apples to David, they had an equal number of apples.
S [2u][2u][2u][1u] --> (7u)
D [2u][2u][2u][1u] --> (7u)

12u - 7u --> 450
5u --> 450
1u --> 90

a)

2u --> 2*90 = 180

the number of apples that David had at first = 180

b)

7u --> 7*90 = 630

630/2 = 315

the number of apples that David gave away = 315

[tracywham]

Thank you for your answer. I du\on’t quite understand. Where does the 2u and 12u comes from Siti?

[jieheng]

tracywham:

Thank you for your answer. I du\\on't quite understand. Where does the 2u and 12u comes from Siti?

Method 1

Siti had 6 times as many apples as David at first

If we assume D --> 1u , then S --> 6u , total (D+S) --> 7u

In the end , they had an equal number of apples

D --> 3.5u and S --> 3.5u after S gave 2.5u to D

2.5u --> 450
1u --> 180

For this method , you will have the decimal points , 3.5u and 2.5u .

Method 2

Siti had 6 times as many apples as David at first

I assume D --> 2u , then S --> 12u , total (D+S) --> 14u

In the end , they had an equal number of apples

D --> 7u and S --> 7u after S gave 5u to D

5u --> 450
1u --> 90

2u --> 2*90 = 180

For this method , you will have the whole numbers , 7u and 5u