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What is 15*9.

Guest Oct 10, 2017
 #1
avatar+84 
+1

\(15*9=135\)

ChowMein  Oct 10, 2017
 #2
avatar+3270 
+1

135, break it up

tertre  Oct 10, 2017
 #3
avatar+2257 
+2

This may help, if multiplying by 9 mentally is difficult. A lot of these mental tricks I wish I knew earlier on.

 

\(15*9\) Let's make it simpler. 
\(15(10-1)\) Obviously, this is the same thing. Now, distribute the 15 to both terms.
\(15*10-15*1\) Now, simplify. This is much easier, don't you think?
\(150-15\) And just in case borrowing is another mental headache...
\(150-(20-5)\) Yet again, I have not changed the expression at all. 
\(150-20+5\) Simplify.
\(130+5\)  
\(135\)  
   

 

This may look like a lot of steps, but all we are doing is making the problem easier. With practice, this will simplify multiplication with large numbers.

TheXSquaredFactor  Oct 10, 2017

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