Try something a bit harder:
A dress is marked up (16 2/3 %) to a final price of $140. What is the original price of the dress?
(16 2/3 %) is on the memorization list; it is equal to 1/6. Adding 1/6 of a number to itself is the same thing as multiplying by 1+ 1/6 = 7/6. Call the original price x and set up and equation to solve.
x + (1/6x) = 140
(7/6x) = 140
x = (6/7) 140
= (6/7) 140 [divide by denominator to get (6 * 20)]
= 120
Therefore, the original price is $120.
My question is:
The book moves from
x + (1/6x) = 140
to
(7/6x) = 140
without explanation.
What are the steps to make that jump?