Q&A - P3 Math

[jwxh]

tks everyone!

[Yerdua]

Hi hi,

Need help with this qn:
how many 4-digits numbers can you make using each of the following digits once: 2,2,5,9?

Is there a formula to get the answer fast or do we have to list all number out as working?

Thanks!

[MathIzzzFun]

Yerdua:

Hi hi,

Need help with this qn:
how many 4-digits numbers can you make using each of the following digits once: 2,2,5,9?

Is there a formula to get the answer fast or do we have to list all number out as working?

Thanks!

Hi

for p3, students are taught to list out the numbers.

for maths olympiad students, they will be taught the \"shortcut\"
number of 4 digit numbers = 4!/2!= 12
4! = 1 x 2 x 3 x 4, 2! = 1 x 2

Let the 4 digit number be ABCD, we can choose any of the 4 digits for A,
then we will be left with only 3 digits to choose for B, and then 2 choices for C and finally 1 choice for D
so, number of 4 digit numbers = 4 x 3 x 2 x 1 = 24
but since there are two \"2\"s, there will be double counting of the \"2\"s. The \"2\"s can be arranged in 2 ways so we have to divide by 2 to get the final answer --> 24/2 = 12

cheers.

[Yerdua]

Hi mathsizzzfun,


Thanks for ur prompt and clear reply!

Went to google for the answer and got even more blur cos of the two '2's. Thanks a lot!

[chloecube]

Yerdua:

Hi mathsizzzfun,


Thanks for ur prompt and clear reply!

Went to google for the answer and got even more blur cos of the two '2's. Thanks a lot!

:imcool: this is like buying 4D...

[Yerdua]

Another qns :oops:


Ms Lee buys some sweets.
If she gives each pupil 5 sweets, she is left with 16 sweets.
If she gives each pupil 8 sweets, she is short of 5 sweets.
How many pupils does Miss Lee have?

Thanks!!

[Sun_2010]

Between case 1 and 2

the no of excess sweets each pupil gets = 8-5 = 3

This excess is provided by the 16 extra in case 1
and the 5 short in case 2 = 16+5= 21

therefore, No of pupil = 21 divided by 3 = 7

Hope my explanation is clear

[Yerdua]

Hi sun_2010,


I got ur explanation after some thinking. It’s like alegbra.
Can I do this qn via model as ds is unlikely to understand it…

Thks thks!

[HAPPYH]

Sun_2010:

Between case 1 and 2

the no of excess sweets each pupil gets = 8-5 = 3

This excess is provided by the 16 extra in case 1
and the 5 short in case 2 = 16+5= 21

therefore, No of pupil = 21 divided by 3 = 7

Hope my explanation is clear

I think this is the olympiad method.

[Yerdua]

WCW:

Yerdua:

Another qns :oops:


Ms Lee buys some sweets.
If she gives each pupil 5 sweets, she is left with 16 sweets.
If she gives each pupil 8 sweets, she is short of 5 sweets.
How many pupils does Miss Lee have?

Thanks!!

http://i44.tinypic.com/15ezrtl.jpg\">

Why didnt i think of guess and check method!? Thks thks to all kind folks!