Sarah got 90% on her math test. if the test was worth 180 points, how many points did sarah get? 200 171 170 162

The answer is:  [D]:  " 162 " .
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Note:   
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90% = 90/100 = 9/10 = 0.9 ;

90% of 180 = 0.9 * 180 =   162 .
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The answer is:  " 162 " .
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Alternate method:
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90% = 90/100 = 9/10 .

9/10  * 180 =  *  ; 

The "10" cancels out to a "1" ; and the "180" cancels to an "18" ; 

     → {since:  " 180 ÷ 10 = 18 " ;  and since:  " 10 ÷ 10 = 1 " } ; 

And we can rewrite as follows:
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  *   = 9 * 18 = 162 .
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The answer is:  " 162 " ;  which is:  Answer choice:  [D]:  " 162 " .
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First, find 10% of 180 by dividing it by 10. 
You get 18. 
Multiply it by 9 to get 90% of the points. 
Sarah earned 162 points on her test. 
Hope this helps!