Question 1131129
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Here is an alternative to the standard method for solving "working together" problems that the other two tutors have shown.<br>
Consider the least common multiple of the two times given, 4 hours and 10 hours.  The least common multiple is 20 hours.<br>
Bob can plant a garden in 10 hours, so in 20 hours she can plant 2 of those gardens.<br>
Together, Bob and her son Andrew can plant the garden in 4 hours, so in 20 hours together they could plant 5 of those gardens.<br>
So in those 20 hours Bob can plant 2 of the gardens, and Bob and Andrew together can plant 5 of them; that means in 20 hours Andrew alone can plant 3 of them.<br>
And so the time Andrew alone takes to plant the one garden is 20/3 hours, or 6 2/3 hours.