singaporeolevelmathsp&c | singaporeolevelmaths http://www.singaporeolevelmaths.com Simple Tips for Better Maths Results! Thu, 05 Jan 2012 14:02:12 +0000 en hourly 1 http://wordpress.org/?v=3.0.4 A-Math P & C Clarification http://www.singaporeolevelmaths.com/2007/10/04/a-math-p-c-clarification/ http://www.singaporeolevelmaths.com/2007/10/04/a-math-p-c-clarification/#comments Thu, 04 Oct 2007 02:27:00 +0000 Ai Ling http://singaporeolevelmaths.com/2007/10/04/a-math-p-c-clarification/ Another question from O Level Additional Mathematics (A-Math).

lijun(: said…
hey. i just want to clarify something that i’m not very sure of.

is nCr x r! = nPr ??

By definition,

nCr = nPr/r!

Well, I never remember this ‘rule’
For example, find the number of ways to form a 3 letter word from a,b,c,d,e

Student #1:
5C1*4C1*3C1

Student #2:
5P3

Both answers are correct though different approaches are taken, so no need to remember the ‘rule’

:)

]]> http://www.singaporeolevelmaths.com/2007/10/04/a-math-p-c-clarification/feed/ 1 A-Math More P & C Qn! On forming numbers http://www.singaporeolevelmaths.com/2007/09/25/a-math-more-p-c-qn-on-forming-numbers/ http://www.singaporeolevelmaths.com/2007/09/25/a-math-more-p-c-qn-on-forming-numbers/#comments Tue, 25 Sep 2007 03:41:00 +0000 Ai Ling http://singaporeolevelmaths.com/2007/09/25/a-math-more-p-c-qn-on-forming-numbers/ Another question from O Level Additional Mathematics (A-Math).

How many even 5-digit numbers more than 50000 can be formed using the digits, 1,2,3,4,5,6,7 if no digit is to be repeated?

Conditions
#1: Even
#2: 5-digit number
#3: no digit is to be repeated

Case 1:When the first digit is odd (must be more than or equal to 5)

2C1 * 5P3 * 3C1

Logic & Reasoning:

first digit: either 5 or 7 so 2C1
last digit: either 2,4 or 6 so 3C1
the remaining 3 digits can be choosen from the leftover 5 numbers so 5C1*4C1*3C1 also = 5P3

Case 2:When the first digit is even

5P3 * 2C1

Logic & Reasoning:

first digit: 6 so no need to choose just put!
last digit: either 2 or 4 so 2C1
the remaining 3 digits can be choosen from the leftover 5 numbers so 5C1*4C1*3C1 also = 5P3

Total even 5-digit numbers more than 50000 can be formed using the digits, 1,2,3,4,5,6,7 if no digit is to be repeated = Case 1 + Case 2 = 480

:)

]]> http://www.singaporeolevelmaths.com/2007/09/25/a-math-more-p-c-qn-on-forming-numbers/feed/ 2 A-Math P & C Qn! http://www.singaporeolevelmaths.com/2007/09/22/a-math-p-c-qn/ http://www.singaporeolevelmaths.com/2007/09/22/a-math-p-c-qn/#comments Sat, 22 Sep 2007 11:11:00 +0000 Ai Ling http://singaporeolevelmaths.com/2007/09/22/a-math-p-c-qn/ The no. of applicants for a job is 15. (i)Calculate the no. of ways in which 6 applicants can be selceted for the interview.

The six selected applicants on a particular day. (ii)Caluculate the no. of ways in which the order of the six interviews can be arranged.

Of the 6 applicants, 3 have backgrounds in business, 2 have backgrounds in education and 1 has a background in recreation. Calculate the number of ways in which the order of the 6 interviews can be arranged, when applicants having the same background are interviewed in succesion.

Who’s up for this challenge?

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Of the 6 applicants, 3 have backgrounds in business, 2 have backgrounds in education and 1 has a background in recreation. Calculate the number of ways in which the order of the 6 interviews can be arranged, when applicants having the same background are interviewed in succesion.

BBB EE RSo there are 3 groups of people and there are 3! ways of arranging these 3 groups
Within BBB group, there are 3! ways of arrange these 3 B people, similar within EE group, there are 2! ways of arrange these 2E people
so Total = Arrange Big Groups * Arrange within each group = 3! * 3! * 2!

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