Consider the sets Tn = {n, n + 1, n + 2, n + 3, n + 4}, where n = 1, 2, 3,...., 78. How many of these sets contain 6 or any integral multiple thereof (i.e., any one of the numbers 6, 12, 18, ...)?  Select the correct option
A) (a) 80  B) (b) 81  C) (c) 82  D) (d) 65  E) (e) 84
T1: 1,2,3,4,5   T2: 2,3,4,5,6   T3: 3,4,5,6,7   etc.   means that every multiple of 6 will be involved in 5 sets. We have (78-6)/6+1= 
<gadget id="calculator">(78-6)/6+1</gadget>
<output>13</output>
13 such multiples.   So, final number of sets is  13*5= 
<gadget id="calculator"> 13*5</gadget>
<output>65</output>
65   Answer: (d) 65
<result>D</result>
Consider the sets Tn = {n, n + 1, n + 2, n + 3, n + 4}, where n = 1, 2, 3,...., 78. How many of these sets contain 6 or any integral multiple thereof (i.e., any one of the numbers 6, 12, 18, ...)?