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Article:
A Rough Guide to Everyday Mental Calculation! by: Murdo Macleod 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 × 70 = 21000 cents = $210. --- TIP -------------------------------------------------- When multiplying numbers ending in zeros e.g. 10 x 100 = 1000: you always end up with the number of zeros added. So 1000 x '30
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