Here’s and example of a SMART MATH problem for RATIO PROPORTION.
Problem
A tank normally filled in 8 hours takes 2 hours longer owing to a leak. If the tank is full the leak shall empty in _________ hours?
- 16
- 20
- 25
- 40
- 45
The Usual Method
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It takes 8 hours for the tank to be filled, so of the tank will be filled in 1 hour.
Owing to the leak, the tank is filled in 8 + 2 = 10 hours, so of the tank will be filled in 1 hour.
Let the leak empty the tank in ‘x’ hours, so of the tank will be emptied in 1 hour.
hours.
(Ans: 4)
Estimated Time to arrive at the answer = 45 seconds.
Using Technique
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Since tank is filled in 1 hour by the inlet working alone and
of the tank is filled in 1 hour by keeping both the inlet and the leak open, the time needed for the outlet to empty the tank should be both a multiple of 8 and 10. (Note:
and
) The only option satisfying this criteria is option ‘4’.
(Ans: 4)
Estimated Time to arrive at the answer = 10 seconds.
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