Video: Combining Opposite Quantities to Solve Word Problems

In Yakutsk, the temperature in February is −40°F. A weather forecast predicts that a warming trend will increase the temperature to 0°F. If the temperature increases with an average of 10° per week, how many weeks will it take to reach 0°F?

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Video Transcript

In Yakutsk, the temperature in February is minus 40 degrees Fahrenheit. A weather forecast predicts that a warming trend will increase the temperature to zero degrees Fahrenheit. If the temperature increases with an average of 10 degrees per week, how many weeks will it take to reach zero degrees Fahrenheit?

In order to solve this problem, we need to look at a number line from negative 40 up to zero, as the initial temperature was negative 40 and the final temperature was zero. We are told that the temperature increases 10 degrees per week.

Therefore, at the end of week one, we need to add 10 to negative 40. Negative 40 plus 10 is equal to negative 30. Therefore, the temperature at the end of the first week is negative 30 degrees Fahrenheit. Negative 30 plus 10 is equal to negative 20. Therefore, the temperature at the end of week two is negative 20. Adding 10 to negative 20 gives us negative 10. Therefore, the temperature at the end of week three would be negative 10 degrees Fahrenheit. Negative 10 plus 10 is equal to zero. Therefore, the temperature at the end of the fourth week is zero degrees Fahrenheit.

We can therefore say that if the temperature increases with an average of 10 degrees per week, it will take four weeks to reach zero degrees Fahrenheit from the initial temperature of negative 40 degrees Fahrenheit.

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