A Math Journey Under the OCEAN Hilary Koll Steve Mills Crabtree Publishing Company www crabtreebooks com
MISSION 1 LEARNING TO DIVE Your first mission is to make sure you are ready to dive so you can explore the underwater world safely LEARN IT ABOUT NEGATIVE NUMBERS 04 Negative numbers are numbers that are less than zero Positive numbers are numbers that are greater than zero The surface of an ocean is called sea level To measure how high a mountain is or how deep something is under the ocean we start our measurement from sea level If sea level is at zero then each meter below sea level can be described as a negative number One meter below sea level is written as 1 two meters below is 2 and so on You know that the number 20 is lower than 30 but it works the opposite way for negative numbers The number 20 is actually higher than 30 See for yourself on the number line shown to the right When diving or rising from an underwater position count up or down the number line For example if you are at 20 m and dive five meters lower count downward from 20 to 25 40 30 20 10 0 10 20 30 40 sea level
To find how far two negative numbers are apart on a number line you can count the interval or the distance between the two numbers The interval will be the same as if the numbers were both positive For example this number line shows that the distance between 30 and 5 is 25 It is the same as the distance between 30 and 5 25 25 30 20 10 0 10 20 30 05 GO FIGURE It’s important to know how far below the surface you are when diving Going too deep can make you sick For your own safety answer these questions using the number lines on these pages to help count 1 Here are some depths below sea level 6 m 32 m 18 m 40 m 25 m a Which of these is the deepest b Put them in order from highest to deepest 2 You dive down to a depth of 35 m 35 meters below sea level a If you rise by 10 m what depth would you be at b From this new position what depth would you be at if you dove down a further 17 m 3 You are at 28 m If you want to get to 7 m how many meters must you rise 4 An octopus is at 31 m How many meters is the octopus below you if you are at a 3 m b 16 m c 2 m above sea level inside the boat
