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by Zipper » Sat Dec 06, 2008 1:27 pm
Simplifying =>

(1001-999).(1001+999)/(101-99).(101+99)=4000/400=10

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by earth@work » Sat Dec 06, 2008 5:01 pm
1001=100+1 & 999=1000-1
101=100+1 & 99=100+1
apply formula: (a+b)^2-(a-b)^2=4ab to both numerator and denominator we get 4000/400=10
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by Chinabean » Sun Dec 07, 2008 12:20 am
hi, looking at the answers, why can't we just estimate? (1000x1000)-(999x1000) = 1mil - 999000 = 1000 and (100x100) - (99x100) = 10000 - 9900 = 100 so 1000 / 100 = 10
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