A two digit number is such that, the sum of its digit is 13.When the digits are interchange, the original number is increased by 9. Find the original number.

Concept: Mathematical Representation

You have a two digit # __ The sum of the two digit # = 13The original # increased by 9 Hence we must find values that sum to 13. *Note they must be independently standing.8+5, 9+6, 7+6 , 6+7 , and etcThe value must also increase by 9 So logically it would be any result that when switched that value would be 76-67= 9.So the value must be 67

To find the number of shoes the store had at the start, you will write the problem out and then work backward through this problem to solve for x, the starting amount.

If 64% of their inventory was sold, then 36% was not.

0.36x - 50) = 288; divide by 0.36 on both sides
x - 50 = 800; add 50 to both sides
x = 850

The store started with 850 pairs of shoes.