21 set 3

[radhika1306]

At a certain food stand, the price of each apple is $0.4 and the price of each orange is $0.6. Mary selects a total of 10 apples and oranges from the food stand, and the average (arithmetic mean) price of the 10 pieces of fruit is $0.56. How many oranges must Mary put back so that the average price of the pieces of fruit that she keeps is $0.52?
(A) 1
(B) 2
(C) 3
(D) 4
(E) 5

[gabriel]

At a certain food stand, the price of each apple is $0.4 and the price of each orange is $0.6. Mary selects a total of 10 apples and oranges from the food stand, and the average (arithmetic mean) price of the 10 pieces of fruit is $0.56. How many oranges must Mary put back so that the average price of the pieces of fruit that she keeps is $0.52?
(A) 1
(B) 2
(C) 3
(D) 4
(E) 5

let the number of oranges be "x" .. then the number of apples = 10-x ..

So, we have (0.6*x+0.4(10-x))/10= 0.56 .. solve this for x and we get that there are 8 oranges and 2 apples ..

.. now remove "a" number of oranges to make the avg 0.52 ..

so, we have (0.6(8-a)+0.4*2)/(10-a) = 0.52 ..solve for a .. and u get a = 5 .. so the answer is E ..

[radhika1306]

Thank you