Question 1190160
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The other tutor showed a solution using the standard algebraic method.  Here is an alternative method.<br>
Consider the least common multiple of the two times, which is 28 hours.<br>
In 28 hours, the two pipes together could fill 28/4=7 of those tanks; in 28 hours the large pipe alone could fill 28/4=7 of those tanks.<br>
That means in 28 hours the smaller pipe could fill 7-4=3 of those tanks; and that in turn means it would take the smaller pipe 28/3 hours, or 9 1/3 hours, to fill the one tank by itself.<br>
ANSWER: 9 1/3 hours<br>