.
Let t be the time walking to grandma, in hours
Then the time riding back is (t-1) hours, according to the problem.
The distance is the same for both routes, so you write this distance equation
4t = 8*(t-1).
Next you simplify and solve it
4t = 8t - 8
8 = 8t - 4t
8 = 4t
t = = 2 hours. ANSWER
Solved.
It was formal algebra solution.
You can solve the problem MENTALLY, too.
The speed back is twice the speed going there.
So, the time going there is twice the time going back.
The difference of these times is 1 hour.
So, the longer time is 2 hours.
You get the same answer.
Solved (in 2 ways).
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Post solution note added after reading the post by @greenestamps.
My approach to teaching in this web-site / (forum) is different from that of @greenestamps.
My starting point is that the students come to this forum to get help in Algebra -
they want FIRST to be TOUGHT in Algebra.
So my first intention and my first concern is to present them an Algebra solution and Algebra approach.
After that, when it is appropriate, I give them a mental solution by reasoning.
It is NOT ALWAYS appropriate to combine both approaches in one post.
The "golden rule" of good teachers is: tell students TRUTH and ONLY TRUTH, but not "all the TRUTH" at once.
Not "all the TRUTH" at a time.
All the truth should go to students gradually with time
(and according with their ability to absorb this truth)
and "by parts".