# SOLUTION: Jay realizes he needs a mark of 100% on his next test in order to achive a 90%average for all his tests.However if he gets a mark of 70% on the next test,his average will be 87%.Af

Algebra ->  Algebra  -> Probability-and-statistics -> SOLUTION: Jay realizes he needs a mark of 100% on his next test in order to achive a 90%average for all his tests.However if he gets a mark of 70% on the next test,his average will be 87%.Af      Log On

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 Click here to see ALL problems on Probability-and-statistics Question 585559: Jay realizes he needs a mark of 100% on his next test in order to achive a 90%average for all his tests.However if he gets a mark of 70% on the next test,his average will be 87%.After he writes the next test,how many tests will he have written? Answer by ankor@dixie-net.com(15649)   (Show Source): You can put this solution on YOUR website!Jay realizes he needs a mark of 100% on his next test in order to achieve a 90% average for all his tests. However if he gets a mark of 70% on the next test,his average will be 87%. After he writes the next test,how many tests will he have written? : Let n = total number of tests Let a = average of the test already taken : Get 100 on the last test equation = 90 a(n-1) + 100 = 90n : Get 70 on the last test equation = 87 a(n-1) + 70 = 87n : Use elimination here a(n-1) + 100 = 90n a(n-1) + 70 = 87n --------------------subtraction eliminates a(n-1), find n 0 + 30 = 3n n = 10 total tests taken : : If you wish to prove this to yourself, solve for a in one of the equations, then check the average in the other equation 9a + 100 = 90(10)