Simon Kolz

A weblog by Simon Kolz

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

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

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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