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# Mental Math for Multiplication/Division Equations

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Practice Mental Math for Multiplication/Division Equations

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Diving In

Credit: Open Science Federation

The ocean is one of the Earth’s last frontiers. Reefs, shipwrecks, strange landscapes, and rare creatures lurk in its depths, waiting to be explored by a brave diver. Diving is an exciting sport, but it also comes with many risks. Divers must keep careful track of their oxygen supplies. They need to know how to avoid dangerous underwater situations. And, even when they leave the water, divers must fear the bends.

#### Time, Air, and Pressure

Divers suffer decompression sickness, also known as “the bends,” when they return to the surface too quickly. As divers descend into the sea, the pressure exerted by the water on their bodies increases with their depth. This high pressure at the bottom of the ocean causes gas to dissolve into a diver’s blood. If the diver comes back up too quickly, the gas rapidly leaves the blood in bubbles that travel through the diver’s body. These air bubbles can cause headaches, joint pain, skin rashes, seizures, paralysis, or even death. Divers therefore need to time themselves so that they rise slowly. They can go no more than 10 meters a minute, and they must periodically stop and rest at various depths.

Credit: Scott Sanchez/NOAA
Source: http://commons.wikimedia.org/wiki/File:Scuba_diver1.jpg

But divers must also keep in mind that they have a limited air supply. They need to be able to do mental math so they can calculate how much time it will take them to make their ascent, and whether they have enough air for the trip. A diver who takes too long and uses all his oxygen will be caught in a bad situation.

#### Explore More

Watch the videos below to learn about two record-breaking dives and the tradition of the haenyo, the incredible women freedivers of South Korea's Jeju Island.

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