### Where did the mental math go?

Recently I saw this kind of problem used as an example; it went something like this:

We're in the grocery store. We're going to buy 6 watermelons, and divide each of them into fourths. How many slices will we get?

I want you to think hard :) ... and find the answer to that question. Also note HOW you found it...

Got it? Now listen how it was solved in this particular mathematics tutorial:

They changed a fourth into its decimal equivalent, 0.25, and proceeded to divide 6 by 0.25 - going thru the motions of multiplying both dividend and divisor by 100 before getting to the long division of 600 ÷ 25, and then finally onto the answer!!!

What happened to mental math?
What happened to solving problems with the most efficient and quickest way?

Well here's a suggestion for an example instead of that one:

You can solve this by going 200 ÷ 0.42.
But even this problem you can estimate the answer this way:

Five notebooks is about \$2. I have hundred times as much money so I should get a little less 500 notebooks with \$200.

In fact, shopping is full of opportunities to practice estimation and mental math. Just try sometime!

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