A book of 100 pages is flipped open. The sum of the facing page numbers can be divided by 5. The quotient is a product of 3 and 7. What are the facing page numbers?
so the facing pages end in 2,3 (why not 7,8?)
So if either page number is a multiple of 21, the product will be too.
42+43 = 85
62+63 = 125
both work
3 ∙ 7 = 21
Therefore, the quotient is 21.
x = sum of the facing page numbers
x / 5 = 21
x = 5 ∙ 21
x = 105
Sum of the facing page numbers is 105.
Only two adjacent numbers which add up to 105 are 52 and 53, so the facing page numbers must be 52 and 53.