We will set a variable, d, to represent the day of the week that January starts on. For instance, if it started on Monday, d + 1 would be Tuesday, d + 2 would be Wednesday, etc. up to d + 6 to represent the last day of the week (in our example, Sunday). The next week would start over at d, and the month would continue. For non-leap years:
If January starts on <u>d</u>, February will start 31 days later. Following our pattern above, this will put it at <u>d</u><u> + 3</u> (28 days would be back at d; 29 would be d+1, 30 would be d+2, and 31 is at d+3). In a non-leap year, February has 28 days, so March will start at <u>d</u><u>+3</u> also. April will start 31 days after that, so that puts us at d+3+3=<u>d</u><u>+6</u>. May starts 30 days after that, so d+6+2=d+8. However, since we only have 7 days in the week, this is actually back to <u>d</u><u>+1</u>. June starts 31 days after that, so d+1+3=<u>d</u><u>+4</u>. July starts 30 days after that, so d+4+2=<u>d</u><u>+6</u>. August starts 31 days after that, so d+6+3=d+9, but again, we only have 7 days in our week, so this is <u>d</u><u>+2</u>. September starts 31 days after that, so d+2+3=<u>d</u><u>+5</u>. October starts 30 days after that, so d+5+2=d+7, which is just <u>d</u><u />. November starts 31 days after that, so <u>d</u><u>+3</u>. December starts 30 days after that, so <u>d</u><u>+5</u>. Remember that each one of these expressions represents a day of the week. Going back through the list (in numerical order, and listing duplicates), we have <u>d</u><u>,</u> <u>d,</u><u /> <u>d</u><u>+1</u>, <u>d</u><u>+2</u>, <u>d+3</u><u>,</u> <u>d</u><u>+3</u>, <u>d</u><u>+3</u>, <u>d</u><u>+4</u>, <u>d</u><u>+5</u>, <u>d</u><u>+5</u>, <u /><u /><u>d</u><u>+6</u><u /><u /> and <u>d</u><u>+6</u>. This means we have every day of the week covered, therefore there is a Friday the 13th at least once a year (if every day of the week can begin a month, then every day of the week can happy for any number in the month).
For leap years, every month after February would change, so we have (in the order of the months) <u></u><u>d</u>, <u>d</u><u>+3</u>, <u>d</u><u>+4</u>, <u>d</u><u />, <u>d</u><u>+2</u>, <u>d</u><u /><u>+5</u>, <u>d</u><u />, <u>d</u><u>+3</u>, <u>d</u><u /><u>+6</u>, <u>d</u><u>+1</u>, <u>d</u><u>+4</u>, a<u />nd <u>d</u><u>+</u><u /><u /><u>6</u>. We still have every day of the week represented, so there is a Friday the 13th at least once. Additionally, none of the days of the week appear more than 3 times, so there is never a year with more than 3 Friday the 13ths.<u />
Answer:
I don't know how to explain the math, but I know the answer is 115 women for every 100 men.
17.5x12=210
210 divided by 14=15
15x2.50=37.5
37.5
17.5 is feet so you need to divide by 12 for inches which gets 210 and you need each necklace to be 14 inches so you need to divide 210 by 14 which is 15 each necklace costs 2.50 so you multiply 2.50x15
You get 37.5
