Compatible Number Estimating

Date: 01/31/2002 at 20:23:16
From: Matt Ward
Subject: Compatible numbers to estimate quotient

My homework is on compatible numbers to estimate quotients - for 
example, 1,625 divided by 38. My Mom and Dad don't understand it 
either. 

Please help me to understand it. 
Thanks,
Matt

Date: 01/31/2002 at 23:30:36
From: Doctor Peterson
Subject: Re: Compatible numbers to estimate quotient

Hi, Matt.
       _______
    38 ) 1625

You want to replace 38 with a nearby number that divides easily into 
something near 1625. (That's what "compatible" means: they play well 
together.) Try just rounding it up to the nearest 10:
       _______
    40 ) 1625

Is there a simple multiple of 40 near 1625? Yes, since 4 times 4 is 
16, 40 times 40 is 1600. So our compatible numbers are

       ____40_
    40 ) 1600

Our estimate is 40. The actual quotient is 42.76, so we're not too far 
off.

Here is a brief discussion in our archives:

   Compatible Number Method for Estimating
   http://mathforum.org/dr.math/problems/salman.09.10.01.html   


- Doctor Peterson, The Math Forum
  http://mathforum.org/dr.math/