I need help with a math word problem - not the answer - just the steps?

Question

Girl completed 20 hrs of comm svc. Worked @ a soup kitchen for 3/7 of the time and picked up litter 1/4 of the time. The rest of the hours she spent tutoring. How much time did she spend tutoring?

Answer 1

First, find the common denominator for 3/7 and 1/4 then translate to a realtive fractions CD=28, 12/28 and 7/28, then add the two together: 19/28
Take the new fraction repesenting the total time spent(19/28) and subtract from the whole fraction of 28/28 -19/28 =9/28
9/28 of the time was spent tutoring.
Lets turn that into hours, 9/28=x/20, so, 9x20 divided by28=6.42 hours
The key was to find the common denominator.

Answer 2

For any of these kinds of questions you usually want to first assign a variable to the thing you are trying to find out, so

let t=time spent tutoring

then you need to write algebra equations that say the same thing as the word sentences in the problem

since 20 hours is the whole time
3/7 * 20 is how long she worked at the soup kitchen
1/4 * 20 is how long she picked up litter

the algebra way of writing the whole equation is:

3/7 *20 + 1/4 *20 + t = 20
then you solve for t

the arithmetic way is to do just calculate the soup time and the litter time and subtract both from 20

3/7 * 20 = 8.57
1/4 * 20 = 5

20 -5 - 8.57 =

Answer 3

Divide 20 by 7, then multiply the answer by 3.That is the soup kitchen. 20 divided by 4 = the time picking up litter. Add these two, then subtract from 20, that will be the tutoring.

Answer 4

20 - 3/7(20) - 1/4(20) = your answer