SOLUTION: Rahul average goes by 1 after scoring 21. His average goes by 2 more after the next score of 35. what is the total runs scored by rahul including 21 and 35 ?

Algebra ->  Average -> SOLUTION: Rahul average goes by 1 after scoring 21. His average goes by 2 more after the next score of 35. what is the total runs scored by rahul including 21 and 35 ?      Log On


   



Question 990633: Rahul average goes by 1 after scoring 21. His average goes by 2 more after the next score of 35. what is the total runs scored by rahul including 21 and 35 ?
Answer by anand429(138) About Me  (Show Source):
You can put this solution on YOUR website!
Let total runs scored before = x
No of innings = y
Avg. = x/y
After scoring 21,
Avg. = (x+21)/(y+1) which should be equal to (x/y) + 1
or, %28x%2B21%29%2F%28y%2B1%29+=+%28x%2Fy%29+%2B+1+
=> y%28x%2B21%29+=+%28y%2B1%29%2A%28x%2By%29
=> xy+%2B+21y+=+xy+%2B+y%5E2+%2B+x+%2B+y
=> y%5E2+-+20y+%2B+x+=+0+ ------------------------(i)
Similarly,
%28x%2B21%2B35%29%2F%28y%2B2%29+=+%28x%2Fy%29+%2B+3
=> yx+%2B+56y+=+xy+%2B+2x+%2B+3y%5E2+%2B+6y
=> 3y%5E2+-+50y+%2B+2x+=+0 -----------------------(ii)
Multiplying (i) by 2, we get,
2y%5E2+-+40y+%2B+2x+=+0+ ------------------------(iii)
Subtracting (iii) from (ii)
y%5E2+-10y+=+0
=> y = 10 (Since y can not be 0)
Putting in (i)
100-200 + x = 0
=> x = 100
So runs scored including 21 and 35 = 100 +21 +35 = 156