Question
A boat can travel 8 km more in downstream than that in
upstream, in 4 hours while the difference between the time taken by the same boat to travel 120 km and 90 km, in still water, is 4 hours. Find the approximate time taken by the boat to travel 200 km in downstream and 120 km in upstream.Solution
Let the speed of boat in still water and speed of stream be 'x' km/hr and 'y' km/hr, respectively. According to question; (120/x) - (90/x) = 4 Or, (30/x) = 4 So, x = 7.5 Now, 4 x (7.5 + y) = 4 x (7.5 - y) + 8 Or, 30 + 4y = 30 - 4y + 8 Or, 8y = 8 So, y = 1 So, downstream speed of the boat = (7.5 + 1) = 8.5 km/hr And, upstream speed of the boat = (7.5 - 1) = 6.5 km/hr Required time taken = (200/8.5) + (120/6.5) ~ (24 + 19) ~ 43 hours
- The average of 9 scores is 45. If two new scores are added and their average is 'x', the overall average becomes 20% more than the previous average. Find t...
 The average marks of 35 Spanish students in a mathematics exam is 75. If the marks of their teacher are included, the average increases by 1. Find the...
The average age of 18 girls is 36 years. If the age of two more girls is added the average decreases by half a year. What is the sum of the age of new g...
Rajat aims to save an average of Rs. 750 per month over the course of a year. For the first 8 months, his monthly income was Rs. 3,000, and he spent 80%...
- In a classroom, the ratio of the number of boys, girls, and teachers is 5:4:1, respectively, and the average number of people in each category is 50. What ...
The mean weight of 24 men is 45 kg, while the mean weight of 18 women is 40 kg. Calculate the combined average weight of all the ...
The average of 17 numbers is 48. The average of first 9 numbers is 45 and average of next 9 numbers is 52. If 9th number is excluded, then th...
The average of 10 numbers is 21.8. The average of the last four numbers is 15. If the average of the first five numbers is 23, then what is the value of...
5 positive numbers are written on a piece of paper. Sum of first 3 numbers is 40 and ratio of the 4th and the 5th number is 2:3. If difference between t...
In an examination, the average marks obtained by the students is 80. After correcting the quantitative mistakes, the average of 90 students is reduced t...
