Aptitude - Boats and Streams - Discussion
Discussion Forum : Boats and Streams - General Questions (Q.No. 8)
8.
A boat takes 90 minutes less to travel 36 miles downstream than to travel the same distance upstream. If the speed of the boat in still water is 10 mph, the speed of the stream is:
Answer: Option
Explanation:
Let the speed of the stream x mph. Then,
Speed downstream = (10 + x) mph,
Speed upstream = (10 - x) mph.
 |
36 | - | 36 | = | 90 |
| (10 - x) | (10 + x) | 60 |
72x x 60 = 90 (100 - x2)
x2 + 48x - 100 = 0
(x+ 50)(x - 2) = 0
x = 2 mph.
Discussion:
85 comments Page 9 of 9.
Sharayu said:
4 years ago
36/(10+x) - 36/(10-x) = 90/60.
Take 36common.
36((10+x)-(10-x))/100-x2 = 9/6.
Solve term.
36*2x/100-x2 = 9/x.
Cross multiple the terms,
72x*6 = 900-9x2.
X2+48x-100 = 0.
Take factor,
Get two term x=-50 & x=2.
Take 36common.
36((10+x)-(10-x))/100-x2 = 9/6.
Solve term.
36*2x/100-x2 = 9/x.
Cross multiple the terms,
72x*6 = 900-9x2.
X2+48x-100 = 0.
Take factor,
Get two term x=-50 & x=2.
(2)
Rishek said:
3 years ago
Let's take 2.
Down stream(time taken) - 36/(10+2)= 3hrs.
Up stream (time taken) - 36/(10-2) = 4.5hrs.
Difference = 1.5hrs which is =90min.
So, option A is correct.
Down stream(time taken) - 36/(10+2)= 3hrs.
Up stream (time taken) - 36/(10-2) = 4.5hrs.
Difference = 1.5hrs which is =90min.
So, option A is correct.
(37)
Singh said:
3 years ago
Why you have subtracted 36/ (10-x) -36/ (36+x) ? Please explain.
(13)
Pavani Kappala said:
2 years ago
Since upstream takes 90 minutes more than downstream,
U(time) = 90 mins+ D( time)
Since time = Distance/speed.
D/ S = 90+D/S.
36/(10-x) = 90+36/(10+x).
36/(10-x) - 36/(10+x) = 90/60( converting into hrs)
36(1/10-x-1/10+x) = 3/2,
12((10+x-10+x)/10^2-x^2) = 1/24,
2x(24) = 10^2-x^2,
x^2+48x-10^2 = 0,
x^2+50x-2x-100 = 0,
x(x+50)-2(x+50) = 0,
(x-2)(x+50) = 0,
x=2,-50.
Since we neglect the negative number, then the answer will be 2mph.
U(time) = 90 mins+ D( time)
Since time = Distance/speed.
D/ S = 90+D/S.
36/(10-x) = 90+36/(10+x).
36/(10-x) - 36/(10+x) = 90/60( converting into hrs)
36(1/10-x-1/10+x) = 3/2,
12((10+x-10+x)/10^2-x^2) = 1/24,
2x(24) = 10^2-x^2,
x^2+48x-10^2 = 0,
x^2+50x-2x-100 = 0,
x(x+50)-2(x+50) = 0,
(x-2)(x+50) = 0,
x=2,-50.
Since we neglect the negative number, then the answer will be 2mph.
(11)
Likitha Ganta said:
2 years ago
Speed downstream = (10 + x) * m/h.
Speed upstream = (10 - x) m/h.
36/(10 - x) - 36/(10 + x) = 90/60.
72** 60 = 90(100 - x ^ 2).
x ^ 2 + 48x - 100 = 0.
(x + 50)(x - 2) = 0.
x = 2m/h.
Speed upstream = (10 - x) m/h.
36/(10 - x) - 36/(10 + x) = 90/60.
72** 60 = 90(100 - x ^ 2).
x ^ 2 + 48x - 100 = 0.
(x + 50)(x - 2) = 0.
x = 2m/h.
(2)
Post your comments here:
Quick links
Quantitative Aptitude
Verbal (English)
Reasoning
Programming
Interview
Placement Papers