Showing posts with label number theoryQ. Show all posts
Showing posts with label number theoryQ. Show all posts

Thursday, 17 September 2009

17 September Solutions

Answers
1) b
2) c
3) b
4) a
5) d
6) d
Solutions:
1)
Number of ordered pairs =  1;
because D=5, G=1
Step 1.

a + b + c + d = d + e + f + g = g + h + i = 17

Means, ( a + b + c + d )+ (d +e + f + g )+ (g +h + i ) = 17 +17+17 = 17 x 3 = 51

a + b + c + d + e + f + g + h + i +( d + g ) = 51

Step 2.

But 'a' to ' i ' takes values only from 1 to 9

So a + b + c + d + e + f + g + h + i = sum of the numbers from 1 to 9 = 45

Step 3.

From step 1 and step 2

d + g = 51 - 45 = 6

possible values of d & g are (1, 5), ( 5,1 ), (2,4) & (4, 2 )

( 2, 4 ) & ( 4 , 2 ) are not possible as "a = 4 "

We have to try with other values (1, 5 ) & ( 5 , 1 )

Step 4.
Case1:  When d = 1 and g = 5

1. a + b + c + d = 4 + b +c + 1 = 17

b + c = 12 ; only possible values of b & c are ( 9, 3 ) or ( 3, 9 )

2. d + e + f + g = 1 + e + f + 5 = 17

e + f = 17 - 6 = 11

possible combinations for 11 are ( 2,9 ) ; ( 3,8 ) ; (4,7 ) & ( 5,6 )

Out of the above four combinations nothing is possible beacuse

b & c takes values 3 & 9 g = 5 (assumed) and a = 4 (given).

So, d = 1 & g = 5 is not the solution.

Case 2. When d = 5 and g = 1

1. a + b + c + d = 4 + b + c + 5 = 17

b + c = 17 - 9 = 8

only possible combination is 2 & 6

a + b + c + d = 4 + ( 2 + 6 ) + 5 = 17

2. d + e + f + g = 5 + e + f + 1 = 17

e + f = 17 - 6 = 11

The only possible value is 3 & 8

d + e + f + g = 5 + ( 3 + 8 ) + 1 = 17

g + h + i = 1 + h + i = 17

h + i = 17 - 1 = 16

The only possible value for h & i are 7 & 9

g + ( h+ i ) = 1 + ( 7 + 9 ) + 17

So the values of d = 5 & g = 1
 
2) Let us write number in base of 3.
T1=1;T2=(10)3;T3=(11)3;T4=(100)3
hence T50= (110010)3=327
(10)3 >= 10 in base 3;(10)3= (3+0)10 ie 3 in base 10
(11)3=(3+1)10=(4)10
(100)3=(9)10
now (10)2=2,(11)2=3,(100)2=4 are the respective term numbers
so the 50th term would be (110010)3 as (110010)2=50

3)g(h(g(x)))=2g(x)^2 + 3g(x)
to calculate g(-4) we have to find out x such that h(g(x))=-4
i.e. x^2 + 4x=0 i.e. x=-4
hence we get g(-4)= 2g(-4)^2+ 3g(-4)
hence g(-4)=-1 
as the problem says ‘includes all numbers that are a sum of one or more distinct powers of 3′ so

4) 2x-1=ax^3 + bxy^2 – 1; 2y-1= ayx^2 + by^3 – 1
(2x-1)(2y-1)=(ax^3 + byx^2 – 1)(ayx^2 + by^3 – 1)
after multiplying ,rearranging the terms and using the other conditions given in the problem we can easily get the ans as 4

5)If k1 is the first then k2 will be the (n+2)th toffee k3 will be (2n+3)th toffee. let us assume that in one complete circle there are k consecutive toffees, as there should be no overlap hence the (k+1)toffee shouldnot overlap onto the 1st toffee.
as there are 30 toffees each toffee will be placed at 12degrees
so (k+1)(n+1)12 shouldnt be equal to 360
ie (k+1)(n+1) =! 30
out of the options only for n=12 we cannot have any value of k satisfying (k+1)(n+1)=30
hence there should be 12 toffees in between!!!

17 September Questions

Questions:
1)
A + B + C + D = D + E + F + G = G + H + I = 17 where each letter represent a number from 1 to 9. Find out number of ordered pairs (D,G) if letter A = 4.
a) 0                       b) 1                 c)2                        d) 3                 e) none of these
2)
The sequence 1, 3, 4, 9, 10, 12….. includes all numbers that are a sum of one or more distinct powers of 3. Then the 50th term of the sequence is
a. 252                    b. 283                     c. 327                      d. 360                  e) none of these
3)
Given that g(h(x)) = 2x² + 3x and h(g(x)) = x² + 4x − 4 for all
real x. WHich of the following could be the value of g(-4)?
a)1                     b) -1                          c) 2                 d) -2                   e) -3
4)
If a, x, b and y are real numbers and ax+by = 4 and ax² +by² = 2 and
ax³ + by³= −3
then find (2x − 1)(2y − 1)
a)4                      b) 3                    c) 5                 d) -3          e) cannot be determined.
5)
K1,K2,K3…K30 are thirty toffees. A child places these toffees on a circle, such that there are exactly n ( n is a positive integer) toffees placed between Ki and Ki+1 and no two toffees overlap each other. Find n
a)4                        b) 5                     c) 9                 d) 12                       e) 13
6)
For the n found in previous  question, which of the two toffees are adjacently
placed on the circle? ( All other conditions remaining same)
a) K11 and K13                    b) K6 and K23                   c) K2 and K10              d) K11 and K18
e) K20 and K28