Question

A package of cookies, packed , ate the fourth part at breakfast , then 3/5 at tea time. there are still 18 cookies in the pakage...
¿how many cookies were in the package ?

Answer 1

ok so
1/4 of total eaten
3/4 left
3/5 of 3/4 eaten
9/20 left
18=9/20 of whole
multiply both sides by 20
360=9 of whole
divide both sides by 9
40=whole


40 total originlly

Answer 2

Break fast =  1/4
Tea time =  3/5
Still 18 left.

Fraction left =  1 - (1/4 + 3/5) = 

1/4 + 3/5 =  (1/4)*(5/5) + (3/5)*(4/4) = 5/20 + 12/20 = (5 + 12)/ 20

 = 17/20

Fraction left =  1 - (1/4 + 3/5) =  1 - 17/20 = (20 - 17)/20 = 3/20

Fraction left = 3/20

Assuming total number of cookies in the package is x.

(3/20)x = 18

3x/20 = 18

3x = 18*20

x = 18*20/3 = 120

There were 120 cookies in the package.