27 10 2010
A Rough Guide to Everyday Mental Calculation!
We all need to check a bill from time to time.
The problem is, how do you do it when you’re in a rush, when
you’re under pressure, and when you don’t have a calculator
handy?
Actually, it’s not at all difficult if you know what to look
for. Here’s how to do it…
Example 1
———
Suppose you are ordering some building supplies and you want
to check that the price is about right before you open your
check book.
You order 213 posts at $5.85 per post.
These numbers can be approximated to 200 posts at $6 per
post.
Multiplying 200 and 6 is easy: the expected bill should be
about $1200.
Basically you just look at the figures and round them to the
nearest convenient unit. (That’s why we approximated $5.85
to $6).
Example 2
———
Similarly for 330 pieces of turf @ 65 cents each,
just find 300
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