Karen has exactly 25 minutes where she can complete some tasks before leaving the house. The tasks are exactly three:
Brush her teeth
Take a shower
Get dressed
So if she wants to allocate exact same amount of minutes to each task, she simply has to divide 25 minutes into 3:
25/3 = 8.33 minutes to each task
or she can distribute 8 minutes to two of them and 9 minutes to the third one.
(this in case the teacher wants whole number of minutes for each task)
For the problem: "Mary has 21/5 hours before she needs to meet her friend. she needs to take care of 7 chores before then how much time can she allocate to each chore? "
What is needed is equivalent to what we just solved, but in this case the teacher wants to have students divide fractions instead of integer numbers.
One needs to perform the following division:
21/5 divided by 7
So we need to recall that dividing fractions is the same as multiplying the first fraction as it is times the "reciprocal" of the second fraction. With "reciprocal meaning the second fraction flipped over.
In general terms, the division of two fractions of the form
a/b divided by c/d is evaluated via the product (multiplication):
a/b times d/c (notice the second fraction flipped)
In our case, we have to do:
21/5 divided 7 which is the same as:
21/5 divided 7/1 (notice I am writing 7 as 7/1 )
then the division can be easily evaluated as the product of the fractions (with the second fraction inverted):
21/5 times 1/7 = (21 * 1)/(5 * 7) = 21/35 = 3/5 ( I have reduced the fraction 21/35 to 3/5 by cancelling out the common factor 7 that appears in both numbers)
So, Mary can assign 3/5 of an hour to each of the 7 tasks.