Jasun P.

One-tenth of the cars in a car park are yellow. Another car arrives and now one-ninth of the cars are yellow. How many cars are now in the car park?

One-tenth of the cars in a car park are yellow. Another car arrives and now one-ninth of the cars are yellow. How many cars are now in the car park?

Let No.of yellow cars = x amd Total Cars = Y
Then X/Y = 1/10  => 10X = Y
Since the ratio got increased after the car arrival, it must be an yellow car.
So Yellow cars = X+1 and Total Car = Y+!
(X+1)/(Y+1) = 1/9   =>  9X+9 = Y+1
So 9X + 9 = 10X + 1    => X = 8 and Y= 80
Total Cars will be Y+1 now = 81
Report

12/16/17

By:

Mark M.

Perhaps I am reading your solution incorrectly, yet if the starting total is 80 the number of yellows would be 8, 8/80 = 1/10.
If the total increases by one, the fraction is 8/81 ≠ 1/9.
I have dithered with this algebraically, and got inconsistencies.
y/t = 1/10  ⇒ 10y = t
y/(t+1) = 1/9 ⇒ 9y = t + 1
Solving the system for t, 0 = t + 10!

Mark M (not of Bayport)
Report

08/23/17

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