Guessing an answer

The Problem You have 10,000 to invest over the next year and will put some of the money in an account earning 12 percent (risky) and three times as much as that in an account earning 4 percent (safer). How much interest will you earn  

Some math word problems have answers that just don t seem right. These answers are the ones that definitely need checking. Other answers are just obviously wrong, meaning that the problem needs reworking. 

Math problems sometimes require solving algebraic equations. The algebra is wonderful, but you run the risk of creating some extraneous roots. Extraneous roots or solutions are answers that satisfy the algebraic equation but don t really mean a thing in the situation. 

The Problem If Folabo leaves home and drives 400 miles north while her sister Fatima leaves home at the same time and drives 300 miles east, how far apart are they  

Sometimes a weird answer looks good at first, and it takes careful checking to show that it doesn t work. 

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Thus we want to guess an answer which implies neglecting less important factors. In the case of water, we will at least temporarily assume that its viscosity doesn t change much and so can t be that big of a factor. We also assume that the major effect of pH is a change in drug solubility and not a change in mass transfer coefficient. 

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