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Conference Time: Generalised Case (Posted on 2006-01-19) Difficulty: 5 of 5
Considering a positive whole number X which contains more than one digit, let us define R(X) as the number obtained by reversing the digits of X. Neither X nor R(X) can contain any leading zeroes.

# A Conference commenced on a given day precisely at M*X/ 143 minutes past P o'clock ( but before P+1 o'clock) and concluded at M*R(X) / 143 minutes past Q o'clock ( but before Q+1 o'clock) on the same day ; where 11 >=Q > P >=1 with the proviso that P and Q are whole numbers and M is a positive integer greater than 1.

#It was observed that the hour hand and the minute hand had exchanged places during the respective times of commencement and conclusion of the said conference.

# Determine the total number of distinct choices of the pentuplet (M,X,R(X),P,Q) satisfying conditions of the problem.

NOTE:

(i)Any two choices of the pentuplet are defined to be distinct if they differ in the magnitudes of at least one of the five parameters (viz. M,X.R(X),P and Q).

(ii)It may be noted that Q is always greater than P. For example, (P=2,Q=3) may correspond to valid values for P and Q, but (P=3,Q=2) is not feasible.

  Submitted by K Sengupta    
Rating: 3.0000 (3 votes)
Solution: (Hide)
There are only two pentuplets given by :
(M,X,R(X),P,Q) = (10,684,486,6,9) and (20,342,243,6,9), which satisfies all the conditions of the problem.

EXPLANATION:

From conditions of the problem, keeping in mind that the conference commenced between P o'clock and P+1 o'clock and the conference concluded between Q o'clock and Q+1 o'clock, we obtain:

(A- B/12) = 5Q and (B - A/12) = 5P where A=M*X/143 and
B=M*R(X)/143

or, 12*M*X -M*R(X) = 143 *( 60Q) AND 12*M*R(X)-M*X = 143 *( 60P).

Solving the above system of simultaneous equations ,we obtain:
X = 60(12Q+P)/M and R(X)= 60(12P+Q)/ M........(*)

Since, 11 >=Q > P >=1 with the proviso that P and Q are whole number , substituting (P,Q) = (1,2), (1,3),……..,(10,11) in turn, we obtain a total of 55 distinct quadruplets corresponding to (P,Q,X,R(X)) which are furnished below:

(P,Q,M*X,M*R(X))=(1,2,1500,840),(1,3,2220,900),(1,4,2940,960),(1,5,3660,1020),(1,6,4380,1080),(1,7,5100,1140),(1,8,5820,1200),(1,9,6540,1260),(1,10,7260,1320),(1,11,7980,1380),(2,3,2280,1620),(2,4,3000,1680),(2,5,3720,1740),(2,6,4440,1800),(2,7,5160,1860),(2,8,5880,1920),(2,9,6600,1980),(2,10,7320,2040),(2,11,8040,2100),(3,4,3060,2400),(3,5,3780,2460),(3,6,4500,2520),(3,7,5220,2580),(3,8,5940,2640),(3,9,6660,2700),(3,10,7380,2760),(3,11,8100,2820),(4,5,3840,3180),(4,6,4560,3840),(4,7,5280,3300),(4,8,6000,3360),(4,9,6720,3420),(4,10,7440,3480),(4,11,8160,3540),(5,6,4620,3960),(5,7,5340,4020),(5,8,6060,4080),(5,9,6780,4140),(5,10,7500,4200),(5,11,8220,4260),(6,7,5400,4740),(6,8,6120,4800),(6,9,6840,4860),(6,10,7560,4920),(6,11,8280,4980),(7,8,6180,5520),(7,9,6900,5580),(7,10,7620,5640),(7,11,8340,5700),(8,9,6960,6300),(8,10,7680,6360),(8,11,8400,6420),(9,10,7740,7080),(9,11,8460,7140),(10,11,8520,7860)
-----------------(##)

Now, for any pair of the form (ks, kt) where P=ks and Q=kt, with s and t being relatively prime to each other and k being a positive whole number, we observe that; since P is less than Q, so s is less than t; and consequently, the minimum possible value of (s,t) is (1,2). Consequently, the maximum value of k is 5, whenever(P,Q)=(ks,kt) = (5,10)

Accordingly, by (*), for any given quadruplet (ks,kt,X,R(X)); the g.c.d of M*X and M*R(X) is 60*k, where k = 1,2,3,4,5.

Hence, M must be equal to a divisor of 60*k (including M).

When, g.c.d.(M*X, M*R(X))=60,corresponding to k=1, then:
M=1,2,3,4,5,6,10,12,15,20,30,60.---------(#)

When, g.c.d.(M*X, M*R(X))=120,corresponding to k=2, then:
M= values given in (#) and 8,24,40 ,120.

When, g.c.d.(M*X, M*R(X))=180, corresponding to k=3, then:
M=values given in (#) and 9, 18, 36, 45, 90, 180.

When, g.c.d.(M*X, M*R(X))=240, corresponding to k=4, then:
M=values given in (#) and 8,16,24,40,48,80,120,240.

When, g.c.d.(M*X, M*R(X))=300,corresponding to k=5, then:
M=values given in (#) and 25, 50, 75, 100, 150, 300.

In the light of the foregoing, checking individually for each of the 55 quadruplets in (##), we observe that only the quadruplet
(P,Q,M*X,M*R(X))=(6,9,6840,4860) generates two distinct pentuplets given by:

(M,X,R(X),P,Q) = (10,684,486,6,9) and (20,342,243,6,9)

None of the other 54 quadruplets in (##) generate any pentuplet corresponding to (M,X,R(X),P,Q) which satisfies all the conditions of the problem.

Consequently, there are only two pentuplets given by (M,X,R(X),P,Q) = (10,684,486,6,9) and (20,342,243,6,9), which satisfies all the conditions of the problem.

Comments: ( You must be logged in to post comments.)
  Subject Author Date
re(2): Computer solutionK Sengupta2006-04-20 21:40:23
re(2): Computer solutionMindrod2006-01-26 21:55:56
re: Computer solutionBob Smith2006-01-24 13:36:11
Computer solutionMindrod2006-01-19 22:59:30
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