M4maths Previous Puzzles

13 Jan 2016 Time and distance

A motor boat goes 10 km upstream and back again to the starting point in 55 minutes. Find the speed of the motor boat in still water, if Stream running at 2 kmph

OPtion

1) 18 km/hr
2) 20 km/hr
3) 28 km/hr
4) 26 km/hr
5) 24 km/hr
6) 22 km/hr
7) 16 km/hr
8) 32 km/hr
9) 30 km/hr
10)None of these

Solution

Let he speed of motor boat in still water be x kmph
Speed downstream = (x+2) km/hr, speed upstream = (x-2) km/hr
Therefore 10/x-2 + 10/x+2 = 55/60
11x^2 - 240x - 44 = 0
x = 22
Rate in still water = 22 km/hr
Option 6)

Correct Option: 6 Best Solution (13)

ankita anand   9 years AGO

let speed of motor boat = x
downstream speed = x + 2
upstream speed = x - 2
so,
10/(x + 2)+10/(x - 2) = 55/60
55x^2-1200x-220
x=22

Like? Yes (15) | No (8)  

Shagun Chaudhary   9 years AGO

{10/(x+2)}+{10/(x-2)}=(55/60)
11x^2-240x-44=0
x=22kmph

Like? Yes (8) | No (4)  

Vivek Ratan   9 years AGO

The speed of boat after adding the time taken in upstream and downstream is 22 km/hr

Like? Yes (9) | No (6)  

Ramgopal   9 years AGO

distance/speed=time
10/(x+2) + 10/(x-2)=55/60
x=22kph

Like? Yes (4) | No (3)  

DEBMALYA GHOSAL   9 years AGO

10/x+2 +10/x-2 = 55/60
=> 11*x^2 - 240*x - 44=0
by solveing this equation we get,
x=22
answer 6

Like? Yes (4) | No (4)  

satish ojha   9 years AGO

10(1/a-2. + 1/a+2) = 55/60=11/12

10(2a/ a^2- 4) = 11/12
a =22 km/hr

Like? Yes (4) | No (4)  

sumit kumar   9 years AGO

let the speed of boat in stil water is x
so a/c to the question
10/x-2 + 10/x+2 =55/60
after solving it
x=22km/h
option 6

Like? Yes (1) | No (3)  

richa   9 years AGO

in upstream speed = boat speed -stream speed
in downstream speed =boat speed +stream speed

Like? Yes (1) | No (3)  

Ritesh kumar   9 years AGO

let x is speed of boat
10/(x-2) + 10/(x+2) = 55/60
solving this
11x^2-240x-44=0
solving this
x=22

Like? Yes (2) | No (4)  

GOURANGA SUNDAR MANDAL   9 years AGO

let speed of still water is x
then the total required time to recover 10 km and return the starting point is =(10/x+2) +(10/x-2)
condition respect to qns is :{(10/x+2) +(10/x-2) }= 55/60
calculate this equ ..we get x=22
so option 6 is correct answer

Like? Yes (2) | No (4)  

Yashi Das   9 years AGO

Let the speed of the motorboat in still water be x kmph .Then,
Speed downstream =(x+2) kmph
Speed upstream = (x-2) kmph
10/((x-2) +10/(x+2)=55/60
on solving x=22

Like? Yes (3) | No (6)  

NIKHIL JAIN   9 years AGO

time taken upstream= 10/(x-2)
time taken downstream= 10/(x+2)
total time = 55/60
on solving x= 22

Like? Yes (3) | No (7)  

gunjan   9 years AGO

speed of motor boat in still water be u km/h
speed of motor boat
upwards= u-2
downards= u+2
thus
(10/(u-2))+(10/(u+2))=(55/60)
solving it u=22km/h

Like? Yes (1) | No (7)