Metro systems of the World. World Metro System Facts. THE world's first metro, now the world's oldest system, is the London Underground in England, which is more commonly known as the Tube, which was opened in 1863. At 402 kilometers in length the London Underground is also the world's second longest metro system.
To find out if 90 is an even number, we divided 90 by two. When we did that, we found the answer to be a whole number. If you divide any number, such as 90, by two and you get a whole number, it means that the number is an even number.hen we did that, we found the answer to be a whole number. If you divide any number, such as 90, by two and you get a whole number, it means that the number is an even number.
In that class, one student was left out, so 3 is an odd number. An odd number represents a group of paired items with one left out. In other words, odd numbers aren't evenly divisible by 2. When we added one more student to the class, we got an even number of students. But add yet another one, and we're back to one student left out: So, just like even numbers, we can generate odd numbers by adding 2 to an already odd number. We just did that by adding 2 to the odd number 3.