M4maths Previous Puzzles

22 Jun 2012 solve

x+y+z = 20
3x+4y+z = 48
4x+3y+6z = 96

Values of x, y, z are respectively

OPtion

1) 5, 6, 9
2) 4, 6, 9
3) 6, 5, 9
4) 2, 8, 12
5) 1, 6, 10
6) 2, 7, 6
7) 4, 8, 3
8) 5, 8, 9
9) no solution possible
10) none of these

Solution

on eliminating z from 1st and 2nd eq. we get 2x+3y = 28
similarly eliminating z from 1st and 3rd eq. we get 2x+3y = 24
so no solution

Correct Option: 9 Best Solution (10)

21 Jun 2012 work

Ram can complete a work in 10 days. Shyam can do the same work in 15 days. They start the work together but Ram quit after 2 days of work. How many days are required to complete the remaining work by Shyam.

OPtion

1) 6
2) 8
3) 9
4) 10
5) 12
6) 14
7) 15
8) 16
9) 18
10) none of these

Solution

work of the two persons of 2 day = 2[(1/10)+(1/15)] = 2[1/6] = 1/3
so remaining work = 1-(1/3) = 2/3
so no of days required by Shyam = 2/3/1/15 = 10

Correct Option: 4 Best Solution (0)

19 Jun 2012 percentage

10 % of 10 + 20 % of 20 + 30 % of 30 + 40 % of 40 + ......+ 100 % of 100
is equal to

OPtion

1) 312
2) 345
3) 356
4) 385
5) 398
6) 423
7) 435
8) 456
9) 478
10) none of these

Solution

10*10/100 + 20*20/100 + .........
=1^2 + 2^2 + 3^2 + ...............+10^2
=10*11*21/6 = 385
here we use formula
sum of squares of first n natural numbers = n*(n+1)*(2n+1)/6

Correct Option: 4 Best Solution (0)

18 Jun 2012 sequence

next number of the sequence
1, 9, 36, 100, 225, ...
will be

OPtion

1) 289
2) 243
3) 343
4) 324
5) 349
6) 392
7) 425
8) 441
9) 512
10) None of these

Solution

this sequence is 1^2, 3^2, 6^2, 10^2, 15^2, 21^2

Correct Option: 8 Best Solution (0)

15 Jun 2012 average

Average of 12 positive numbers is 12. On changing one of the number, the new average is 10.8, What will be the difference of the new and previous value of that number

OPtion

1) 9.6
2) 9.8
3) 10.4
4) 10.8
5) 12.6
6) 14.4
7) 14.8
8) 15.2
9) 15.4
10) 16.2

Solution

total of first 12 numbers = 12*12 = 144
total of 12 numbers after changing one number = 10.8*12 = 129.6
so difference = 14.4

Correct Option: 6 Best Solution (0)

14 Jun 2012 percentage

40% of 60 + 60 % of 40 = 50 % of x
x will be

OPtion

1) 96
2) 92
3) 88
4) 84
5) 80
6) 78
7) 75
8) 68
9) 52
10) none of these

Solution

40% of 60 + 60 % of 40 = 50 % of x
so 60*0.4 + 40*0.6 = x*0.5
or 48 = 0.5x
or x = 96

Correct Option: 1 Best Solution (19)

13 Jun 2012 dictionary

100th word of the dictionary formed by using the letters of the word KISHAN

OPtion

1) AKHSNI
2) ASNKHI
3) ASINKH
4) ASHNKI
5) ASKHNI
6) ASHKNI
7) ASNHKI
8) ANSHKI
9) ANKISH
10) none of these

Solution

total no. of words = 720
first 120 words will be started with A
In these 120 words last 24 words will be started with AS
these no. will belong from 97 to 120
in these 24 words first 6 will be started with ASH
these no. will belong from 97 to 102
In these 6 words middle 2 will be started with ASHK
these no. are 99th and 100th
99th word is ASHKIN and 100th word is ASKHNI

Correct Option: 6 Best Solution (0)

12 Jun 2012 rice rice

The cost (per Kg) of 3 qualities of rice are 45, 42 and 35 respectively. The cost (per Kg) of a mixture of 10 Kg of first, 8 Kg of second and 7 Kg of third will be

OPtion

1) 39.86
2) 39.64
3) 40.46
4) 41.24
5) 42.34
6) 42.38
7) 43.46
8) 43.12
9) 44.42
10) none of these

Solution

(45*10+42*8+35*7)/25 = (450+336+245)/25 = 1031/25 = 41.24

Correct Option: 4 Best Solution (7)

11 Jun 2012 odd number

select the different one

OPtion

1) 1843
2) 2594
3) 2687
4) 4987
5) 4128
6) 6591
7) 7428
8) 6523
9) 4148
10) 6752

Solution

2594 ----- 25 9 4
these three are perfect squares of first three prime numbers.

Correct Option: 2 Best Solution (0)

08 Jun 2012 quadratic equation

If k^2+9k-10<0
and k<0
then k belongs to

OPtion

1) (-10, -4)
2) (-14, -5)
3) (-12, -3)
4) (-10, 0)
5) (- 9, 0)
6) (-13, -4)
7) (-12, -2)
8) (- 5, 0)
9) (- 8, 0)
10) none of these

Solution

k<0 means only negative values are possible
and k^2+9k-10 < 0
implies that (k+10)(k-1) < 0
implies that -10 but k is negative so answer will be -10

Correct Option: 4 Best Solution (0)