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| Math Central | Quandaries & Queries |
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Question from Lisa: As an educator in Adult Education, I am preparing a young man for a US Government test. The equation I have trouble with is explaining the following equation. It asks: If it takes A 3 days to dig a certain ditch, whereas b can dig it in 6 days, and C in 12, how long would it take all three to do the job? I know the equation is 1/3 + 1/6 + 1/12 and it equals = 7/12 but I don't understand how it equals 7/12. This simple math eludes me. So the question is not the final answer of 1 and 5/7 of days but where one comes up with the 7/12? Thank You and Happy New! |
We have two responses for you
Hi Lisa,
To add fractions we need their denominators to be equal. Thus for your problem you need to find equivalent fractions for 1/3, 1/6 and 1/12 all of which have the same denominator. With these three fractions you can use the denominator 12 since
and
Thus
Penny
In 12 days, A digs 4 ditches, B digs 2, and C digs 1, so all together they dig 7 ditches. How long does it take them to dig 1 ditch?
Claude
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