A farm has 76 acres of wheat. The farmer can harvest the wheat from 12 acres per day. In how many days will all of the fields be harvested?

1 Answer
Oct 22, 2016

6 1/3 613 days

Explanation:

Let the unknown number of days be xx
color(white)(.).
color(blue)("Using ratio to show why the shortcut method works.")Using ratio to show why the shortcut method works.

(76" acres")/(12" acres") =(x" days")/(1" day")76 acres12 acres=x days1 day

so x=76/12 ->(76-:4)/(12-:4)=19/3 = 6 1/3" days"x=761276÷412÷4=193=613 days
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color(blue)("Using ratios differently")Using ratios differently

The clue is in the wording of 'acres per day' which translates to:
("acres")/("days")acresdays

(12" acres")/(1" day")=76/x12 acres1 day=76x

To maintain the correct ration, if you multiply the top number of a fraction or ratio you must do the same to the bottom number
Note that 6 1/3xx12=76613×12=76

Multiply by 1 but in the form of 1=(6 1/3)/(6 1/3)1=613613

[(12" acres")/(1" day")xx1] =76/x[12 acres1 day×1]=76x

[(12" acres")/(1" day")xx(6 1/3)/(6 1/3)]=76/x[12 acres1 day×613613]=76x

76/(6 1/3)=76/x76613=76x

x=6 1/3" days"x=613 days