coolhabhi wrote:A cricketer made 90 runs in his 12th inning, and his average declined by 5 runs. Find his new average after the 12th innings.

a)127
b)145
c)150
d)180
e)217

We can PLUG IN THE ANSWERS, which represent the average after 12 innings.
Since the average after the 12th inning decreases by 5 runs, the answer choices imply the following options for the average after 11 innings:
127 + 5 = 132.
145 + 5 = 150.
150 + 5 = 155.
180 + 5 = 185.
217 + 5 = 222.

Given that the number of runs made in the 12th inning is a MULTIPLE OF 10, the most likely answer choice is B -- the only option that yields a multiple of 10 for the average after 11 innings.
When the correct answer choice is plugged in, 90 runs will be made in the 12th inning.

Answer choice B:
Total runs after 12 innings = (number of innings)(average per inning) = 12*145 = 1740.
Total runs after 11 innings = (number of innings)(average per inning) = 11*150 = 1650.
Runs made in the 12th inning = (total for all 12 innings) - (total for the first 11 innings) = 1740-1650 = 90.
Success!

The correct answer is B.

I think we can also do the following:

sum of first 11 rounds is 11M

so for the 12 rounds: (11M+90)/12 = M-5

11M+90 = 12M-60 Subtract 11M from both sides and add 60 to both sides

150 = M

Hence M-5 = 150-5 = 145

BINGO!

Brent@GMATPrepNow wrote:

coolhabhi wrote:A cricketer made 90 runs in his 12th inning, and his average declined by 5 runs. Find his new average after the 12th innings.

a)127
b)145
c)150
d)180
e)217

Let F = TOTAL # of runs for the first 11 innings
So, F + 90 = TOTAL # of runs for 12 innings

Let A = Average runs per inning after 12 innings [note: our goal is to find the value of A]
So A + 5 = Average runs per inning after 11 innings [since we're told that, his average was 5 runs MORE after 11 innings]

So, F/11 = A + 5 [total number of runs for 11 innings/11 innings = average runs per inning]
Also, (F + 90)/12 = A [total number of runs for 12 innings/12 innings = new average runs per inning]

We now have two equations with 2 variables:
F/11 = A + 5
(F + 90)/12 = A

Take 1st equation and cross multiply to get: 11A + 55 = F
Take 2nd equation and cross multiply to get 12A = F + 90 . Rearrange to get: 12A - 90 = F

Since BOTH equations are equal to F, we can conclude that 11A + 55 = 12A - 90
Solve to get A = 145

Answer: B

Cheers,
Brent

Avg declined by 5 runs=total drop of 11*5=55 runs.
add to the current score =90+55=145

Suppose the average of the first 11 innings was x.

We know that

(Previous Run Total)/11 = x

and that

(Previous Run Total)/11 = 5 + ((Previous Run Total + 90)/12)

so we have

x = 5 + (11x + 90)/12

12x = 60 + 11x + 90

x = 150

Since x is our old average, our new average = 150 - 5 => 145