Let c=speed of current, so the effective upstream speed against the current is 16-v and with the current downstream is 16+c. The distances travelled are 15 miles in each case.

Distance=speed times time, so time=distance/speed and the combined times for upstream and downstream:

15/(16-c)+15/(16+c)=2, so 15(16+c)+15(16-c)=2(16²-c²), 480=512-2c², c²=(512-480)/2=32/2=16 so c=4mph.

- All categories
- Pre-Algebra Answers 12,323
- Algebra 1 Answers 25,303
- Algebra 2 Answers 10,448
- Geometry Answers 5,189
- Trigonometry Answers 2,642
- Calculus Answers 6,024
- Statistics Answers 3,025
- Word Problem Answers 10,138
- Other Math Topics 6,677

81,769 questions

86,073 answers

2,215 comments

69,559 users