Sign in
Please select an account to continue using cracku.in
↓ →
The average number of copies of a book sold per day by a shopkeeper is 60 in the initial seven days and 63 in the initial eight days, after the book launch. On the ninth day, she sells 11 copies less than the eighth day, and the average number of copies sold per day from second day to ninth day becomes 66. The number of copies sold on the first day of the book launch is
Correct Answer: 49
Let the copies sold on days 1 through 9 be $$d_1,\dots,d_9$$
From the averages:
$$d_1+\cdots+d_7=7\times60=420$$
$$d_1+\cdots+d_8=8\times63=504$$
So $$d_8=504-420=84$$. Then $$d_9=84-11=73$$
The sum from day 2 to day 9 is $$8\times66=528$$
$$d_2+\cdots+d_9=(d_1+\cdots+d_8)-d_1+d_9=504-d_1+73=577-d_1$$
Thus $$577-d_1=528 \Rightarrow d_1=49$$
Click on the Email ☝️ to Watch the Video Solution
Create a FREE account and get:
Book Free CAT Mentorship
Get personalized CAT strategy from a 99%iler
500+ students mentored
OTP Verification
Enter the 6-digit code sent to your phone
Booking Summary
Enter OTP
Didn't receive the OTP?
Educational materials for CAT preparation