David has d books, which is 3

Cydney Seigerman, Magoosh Tutor

Hi Sonika :)

Good questions! We're describing the number of books for the three in terms of the number of books that David has, d.

Let's say that Jeff has j number of books. Since David has three times as many books as Jeff,

3j = d

Now, let's solve for j to describe the number of books Jeff has in terms of d:

3j = d
j = (1/3)d

We can check this is correct using actual values. Let's say that David has 12 books, which means that Jeff has 4 books:

j = (1/3)d
j = (1/3)*12
j = 4 <-- this matches what we said above!

On the other hand, David has half of the number of books as Paula. Another way of saying this is that Paula has double the number of books as David:

p = 2d

Again, let's say that David has 4 books. That would mean that Paula has 8 books (4/8 = 1/2):

p = 2*4 = 8 <-- again this matches what we said just above.

Since we want to solve for the number of books in terms of d (the number of books David has), we must solve for the number of books that Jeff and Paula have, j and p respectively, in terms of d. And that's the process I've shown above!

Hope this clears up your doubts :)

Dec 9, 2016 • Reply