(1/14 - 1/15) : (1/15 - 1/16) * (1/16 - 1/17) : (1/17 - 1/18) = 1 2/7
1) 1/14 - 1/15 = 15/210 - 14/210 = 1/210
2) 1/15 - 1/16 = 16/240 - 15/240 = 1/240
3) 1/16 - 1/17 = 17/272 - 16/272 = 1/272
4) 1/17 - 1/18 = 18/306 - 17/306 = 1/306
5) 1/210 : 1/240 = 1/210 * 240/1 = 240/210 = 8/7
6) 8/7 * 1/272 = 8/1904 = 1/238
7) 1/238 : 1/306 = 1/238 * 306/1 = 306/238 = 9/7 = 1 2/7