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A math student has solved 500 problems and got 350 of them right.

If he now starts getting every problem right, after how many problems will he have got 75% of all his problems right?

 Feb 14, 2021
 #1
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Call   x  the  number of consecutive  problems (after 350)  that  he  needs to solve

 

So

 

(350  + x)  /(500 + x)  =  .75     cross-multiply

 

350 + x  =  .75 ( 500 + x)       simplify

 

350  + x  = 375  +  .75x

 

x - .75x  = 375 - 350

 

.25x  =  25

 

x  =25  /.25   =  100

 

He  will have 75% right  after  350 + 100   = 450  problems 

 

 

cool cool cool

 Feb 14, 2021

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