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.
(b) Use either a proof by contraposition or a proof by contradiction to show that if m and n are integers and mn is even, then m is even or n is even. Answer: An odd number is one of the form 2n+1, where n is an integer.We are given two odd numbers, say 2a+1 and 2b+1. Their product is: (2a+1)(2b+1) = 4ab + 2a + 2b + 1 = 2(2ab + a + b) + 1This last expression shows that the product is odd, since it is of the form 2n+1, with n = 2ab + a + b.b) Use either a proof by contraposition or a proof by contradiction to show that if m and n are integers and mn is even, then m is even or n is even. Answer: An odd number is one of the form 2n+1, where n is an integer.