Expert: Lynn Houston - 7/17/2009

Question
QUESTION: a batsman having a certain average in 11 matches, he scores 129 runs in 12th match and his average increases by 9 runs, what was his average in 11 matches?

ANSWER: x/11 = 129

x+y/12 = 129+9

solve the first eq for x by multiplying both sides by 11

x = 1419  now, insert the value of x into the second eq and solve for y

(1419 + y)/12 = 138  multiply by 12

1419+y = 1656  subtract 1419 from both sides

y = 237  (he REALLY did well in his 12th match, apparently!)

make sense?





---------- FOLLOW-UP ----------

QUESTION: thanx alot . for the quick answer but....


but this isnt the answer i was looking for.....


129 runs are the runs he made in 12th match

What was asked was What was his average in 11 matches???

Answer
I have no idea what question I answered, but it obviously wasn't the one asked.  A good lesson to read your questions closely.

QUESTION: a batsman having a certain average in 11 matches, he scores 129 runs in 12th match and his average increases by 9 runs, what was his average in 11 matches?

let x = total score of 1st 11 matches


x/11 = a
x + 129/12 = a + 9
(x + 129)/12 - 9 = a

x/11 = ((x + 129)/12) - 9

eliminate the fractions by multiplying both sides by (11)(12)

12x  = 11(x + 129)- 9(11)(12)
12x  = 11x + 1419 - 1188
12x - 11x = 1419 - 1188
x = 231

231/11 = 21 (average after 11 games)

To confirm the answer... (231 + 129)/12 should = 21 + 9

In reality though, it is highly unlikely that after averaging 21 runs per match that he would all of a sudden score 129 runs in one match.