Question
A man can go on a motor boat with a speed of 15 km/hour
in still water to a certain upstream point and come back to the starting point in a river which flows at a speed of 5km/hour. Find the average speed of motor boat for total journey?Solution
Let, the speed of boat be b km/hour and speed of current be s km/hour Average speed = 2xy/(x+y) (here, x is speed of downstream and y is speed of upstream)               = (2 (b+s)(b-s))/((b+s+b-s))               = (b2 - s2)/b               = (225 - 25)/15 = 200/15 = (40/3) km/hour Alternate Method :- 
Average speed = (Total distance covered)/(total time taken)               = (2×60)/9 = 120 /9 = 40/3 kmph
A sum of money is invested at 8% simple interest per annum. If the interest earned after 4 years is ₹3200, what is the principal amount?
Mr. X invested Rs. 1200 in two schemes, A and B in the ratio of 7:3, respectively. Scheme A and B are offering simple interest at rate of 9% per annum a...
Rahul invested Rs. ‘x’ at 13% p.a. and Rohit invested Rs. (x + 300) at 12% p.a. If the interest after 3 years is Rs. 1755, find the value of ‘x’...
'X' invested Rs. 18,000, splitting the amount between two SIPs: 'P' offering 8% per annum simple interest and 'Q' offering 10% per annum compound intere...
If ₹5,000 is invested at an annual interest rate of 8% compounded quarterly, at what time will it grow to ₹5,202?
What will be the simple interest on Rs. 6,20,000 from March 30, 2011 to November 04, 2011 at 12 % p.a?
Find the simple interest on Rs. 6500 at 9% per annum for 4 years.
A sum of Rs. 'p' is invested at a compound interest rate of 15% per annum, compounded once every 8 months. After 16 months, the t...
Roshan and Rahul received marks in their quarterly exam in a ratio of 9:8. Additionally, the ratio of marks Roshan obtained in the quarterly exam to the...
A sum doubles in seven years at simple interest. In how many years will the sum become five times the original sum?
