Question 81394
when all the grocery carts escape from the supermarket, it takes Reginald 12 minutes to round them up and bring them back. Because Norman doesn't make as much as Reginald, it takes Norman 18 minutes to do the same job. How long would it take them working together to complete the roundup?
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Let t = time required when they work together
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Let the completed job = 1:
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A simple equation:
{{{t/12}}} + {{{t/18}}} = 1
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Get rid of the denominators, multiplying equation by 36 would give us:
3t + 2t = 36
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5t = 36/5
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t = 7.2 min or 7 + .2(60) = 7 min 12 sec
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Check our solution of t = 7.2 min
{{{7.2/12}}} + {{{7.2/18}}} = 
   .6  +  .4 = 1