M4maths Previous Puzzles

21 Jul 2020 Boats and Streams

The speed of the motor boat in still water is 25/3 m/s.
It goes 75 km downstream and comes back in 9 hours. Find the speed of the current in km/hr.

OPtion

1) 50/9
2) 20
3) 13
4) 13.33
5) 20
6) 15
7) 18
8) 14
9) 12
10) None of these

Solution

Let the speed of the current = 'x' km/hr

Speed of motor boat = 25/3 m/s = (25/3)*18/5 = 30 KM/hr

We have 75/(30+x) + 75/(30-x) = 9
⇒ 75(60/(900-x2)) = 9
⇒ 900-x2 = 500
⇒ x2 = 400
⇒ x = 20km/hr

Correct Option: 5 Best Solution (0)

20 Jul 2020 Simple Interest

A certain sum of money amounts to 7/4 of itself in 6 years. The rate percent p.a. is

OPtion

1) 15.0
2) 12.5
3) 25.0
4) 22.5
5) 12.0
6) 10.0
7) 11.0
8) 14.0
9) 16.0
10) None of these

Solution

R = [100(7/4-1)]/6
=> 100*(3/4)*1/6
=> 100/8 = 12.5

Correct Option: 2 Best Solution (0)

17 Jul 2020 Number

A = (26a^2 + 13a + 9)/a; where A belongs to integer. How many integral solutions of A are possible?

OPtion

1) 2
2) 3
3) 6
4) 9
5) 8
6) 7
7) 10
8) 12
9) 24
10) None of these

Solution

(26a^2 + 13a + 9)/a = 26a + 13 + 9/a

Now we can see that whatever the value of ‘a’, 26a + 13 will always give an integral value.
So, it now depends upon 8/a only

=> a can have any integral value, which is a factor of 9.
The integers, which will satisfy this condition are ±1, ±3, ±9. Thus, in total,a can take 6 values.

Correct Option: 3 Best Solution (2)

16 Jul 2020 Race

In a 100 m race, Ram reaches the final point in 28 s and Rahim reaches in 35 s. By how much distance does Ram beat Rahim?

OPtion

1) 20
2) 5
3) 15
4) 16
5) 25
6) 6
7) 8
8) 7
9) 10
10) None of these

Solution

In this question, we have to find the distance covered by Rahim, after Ram has finished the race
i.e. distance covered by Rahim in (35 – 28 = 7s).
Distance = 100/35 × 7 = 20 m
Ram beats Rahim by 20 m.

Correct Option: 1 Best Solution (0)

15 Jul 2020 Handshakes

In a party there are 24 persons present. If each of them shakes hand with all the other persons,in total how many handshakes will take place?

OPtion

1) 206
2) 216
3) 226
4) 236
5) 256
6) 266
7) 278
8) 286
9) 276
10) None of these

Solution

Out of 24 persons, the first person will shake hand with 23 persons.
The second person will shake hand with 22 persons (because he has already shaken hand with first person).
The third person will shake hand with 21 persons and so on. The second last person shakes hand with only one person. And last will shake hand with none
(because he has already shaken hand with all persons).
In order to find the total number of handshakes you have to add all the natural numbers from 1 to 23 i.e. ∑ 23.
∑23 = 23 x 24/2 = 276 = 276 handshakes.

Correct Option: 9 Best Solution (1)

14 Jul 2020 Age

Sum of age of 6 children born at interval of 6 years is 240. What is the age of youngest child?

OPtion

1) 12
2) 8
3) 5
4) 16
5) 11
6) 25
7) 30
8) 18
9) 4
10) None of these

Solution

Let the ages of children be x, (x+6*1),
(x+6*2).... (x+6*5) years.

=> x + (x+6*1) + (x+6*2)+ (x+6*3) + (x+6*4) + (x+6*5) = 240
=> 6x + 90 = 250
=> x = 25

Correct Option: 6 Best Solution (2)

13 Jul 2020 Profit & Loss

Find the cost price of an item which is sold for Rs. 440 at a loss of 12%.

OPtion

1) 520
2) 600
3) 480
4) 460
5) 560
6) 525
7) 400
8) 500
9) 660
10) None of these

Solution

If CP 100 SP 88
i.e. When SP 88 CP 100
when SP 440 CP = 100*440/88 = 500

Correct Option: 8 Best Solution (4)

10 Jul 2020 Probability

In a bag there are 10 red and 15 blue marbles. Two marbles are drawn in succession without replacement. What is the probability that first is red and second is blue

OPtion

1) 1/2
2) 5/8
3) 2/5
4) 3/4
5) 1/4
6) 1/6
7) 2/7
8) 3/8
9) 2/9
10) None of these

Solution

Probability that first one is red = 10/25 = 2/5

Probability that second one is blue = 15/24 = 5/8

probability that first is red and second is blue = 2/5 * 5/8 = 1/4

Correct Option: 5 Best Solution (0)

09 Jul 2020 Percentage

The price of a flat is decreased from Rupees seventy five lakhs to Rupees sixty lakhs. Find the percentage of decrease.

OPtion

1) 14.29
2) 16.66
3) 25.00
4) 20.00
5) 12.50
6) 10.00
7) 16.00
8) 24.00
9) 19.00
10) None of these

Solution

75000 - 60000 = 15000
% = 15000*100/75000 = 20%

Correct Option: 4 Best Solution (0)

08 Jul 2020 Surface Area

Find the surface area of a cuboid 16 m long, 14 m broad and 17 m high (in m^2)

OPtion

1) 864
2) 868
3) 872
4) 786
5) 687
6) 1468
7) 1486
8) 1406
9) 1496
10) None of these

Solution

Surface area = [2 (16 x 14 + 14 x 17 + 16 x 17)] sq.cm

= (2 x 434)sq.cm = 1468

Correct Option: 6 Best Solution (5)