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.
9 is not an even number. There is an odd 1: Therefore we call 9 an odd number. We cannot take half of a natural number that is odd. We cannot take half of 9 people. The even numbers, then, are the numbers divisible by 2: 2, 4, 6, 8, and so on.The odd numbers are 1, 3, 5, 7, and so on.If you do not know half of some even number, you can find it by decomposing it mentally into two even numbers whose half you do know. We saw how to do that in Section 1, Example 8. Example 1.gain, if a natural number is odd, then we cannot take half of it. Therefore, we will now assume that we are not necessarily dealing with natural numbers, and that 1 is now a continuous unit -- a unit we use to measure -- and that has a half: 1 minute, 1 centimeter, 1 pound, and so on. (Lesson 20 .).