Tips and Tricks of The Day


Record Limit : 

    2020-Apr-03
Ex: In a two digit number, unit digit is 2 more than the ten's digit. Four times of the sum of digit is 3 less than the number. What is the number ?
(A) 20
(B) 36
(C) 35
(D) 50
Trick:
Let the two digit number be 10x + y
10x + y
y = x +2
y –x = 2 ....(I)
(y+x) 4 = 10x + y – 3
4x +4y = 10x + y–3
6x –3y = 3 ........ (II)
From eq. (I) and (II)
x = 3
y = 5
So, number = 35
    2020-Apr-02
Ex: Excluding stoppages, the speed of a bus is 54 km/hr and including stoppages, it is 45 km/hr, for how many minutes does the bus stop per hour?
A)  12 minutes       
B)  8 minutes
C)  10 minutes
D)  5 minutes
Trick:
Stopping per hour = 54 − 45 / 45 × 60 = 9 / 45 * 60 = 12 min.
    2020-Apr-01
Ex:  Two trains with their speeds in the ratio of 3: 4 are going in opposite directions along parallel tracks. If each takes 9 seconds to cross a telegraph post, then the time taken by the trains, to cross each other completely, will be:
(A) 18 seconds
(B) 12 seconds
(C) 9 seconds
(D)  3 seconds
Trick:
L1/3k = 9
L1 = 27 k
and
L2/4k = 9
L2 = 36 k
Now, Required time = (L1 + L2)/ (3k + 4k) = 9 seconds
    2020-Mar-31
Ex: A sum of money at simple interest amount to Rs.8118 in 3 years and to Rs.9449 in 4 years. The sum is-
(A) Rs.4135
(B) Rs.4125
(C) Rs.4120
(D) Rs.4130
Trick:
Simple interest = 9449 – 8118 = Rs.1331
Simple interest in 3 years = 3 × 1331
= Rs.3993
Sum = 8118 – 3993 = Rs.4125 
    2020-Mar-30
Ex: 15 movie theatres average 600 customers per theatre per day. If six of the theatres close down but the theatre attendance stays the same, the average daily attendance per theatre among the remaining theatres is
(A) 1100
(B) 1200
(C) 900
(D) 1000
Trick:
Total customers in 15 movie theatres = 15 × 600 = 9000
Total customers in (15 – 6 = 9) movie theatres now = 9000
Required average number = 9000 ÷ 9 = 1000
    2020-Mar-27
Ex: The monthly salaries of two persons in the ratio 8:9. If each receives an increase of Rs. 20 in the salary, the ratio becomes 25:28. Find their salaries.
A. 500, 560
B. 400, 540
C. 550, 600
D. 480, 540
Trick:
(8x + 20) / (9x + 20) = 25/28
=> x = 60
8x= 8 * 60 = 480 and 9x= 9 * 60 = 540
    2020-Mar-26
Ex: Water flows into a tank which is 200 m long and 150 m wide, through a pipe of cross-section (0.3m x 0.2m) at 20 km/h. In what time will the water level be 8m?
(A) 250       
(B) 200         
(C) 450          
(D) 350
Trick:
Volume of water collected in the tank in 11 hour
⇒0.3×0.2×20×1000 = 1200 m cubic 
If after t hours, the water is at height of 8m, 
1200t = 200×150×8 
⇒t = 200 Hours.
    2020-Mar-25
Ex: The sum of the squares of 3 consecutive odd numbers is 251. Then find the sum of the numbers.
(A) 9
(B) 15
(C) 21
(D) 27
Trick:
Let three odd numbers be 2x – 1, 2x + 1, 2x + 3.
(2x – 1)^2 + (2x + 1)^2 + (2x + 3)^2 = 251
12x^2 + 11 + 12x = 251
12x^2 + 12x – 240 = 0
x = 4, – 5
Numbers are = 7, 9, 11
Required sum = 7 + 9 + 11 = 27
    2020-Mar-25
Ex: The sum of the squares of 3 consecutive odd numbers is 251. Then find the sum of the numbers.
(A) 9
(B) 15
(C) 21
(D) 27
Trick:
Let three odd numbers be 2x
    2020-Mar-24
Ex: A wheel of radius 1.4 m. of a vehicle makes 40 revolutions in 1 min. What is the speed of the vehicle?
(A) 21.12 km/h.
(B) 19.6 km/h.
(C) 22.7 km/h.
(D) 22.4 km/h.
Trick:
Distance covered in 1 revolution = 2 * 22/7 * 1.4 = 8.8 m.
Distance covered in 40 revolutions = 40 × 8.8 = 352 m. = 0.352 km.
Time = 1/60 hr.
Speed = 0.352 / 1/ 60 = 21.12 km/h