Given: Deepti has 49 stamps which are of one-rupee. 50 paise and 25 paise denominations. The total value of her stamps is 23.50.
Asked: If the number of 25 paise stamps is greater than the number of 50 paise stamps and one-rupee stamps together, and the number of one-rupee stamps is less than 50 paise stamps, how many more 25 paise stamps than one-rupee stamps does Deepti have?
Let one-rupee, 50 paise and 25 paisa stamps be x, y & z respectively
1. x + y + z = 49
2. x + .5y + .25z = 23.5
3. z > x+y
4. x < y
z - x = ?
1) - 2)
.5y + .75z = 25.5
2y + 3z = 102
z = (102-2y)/3
(y,z) = {(0,34),(3,32),(6,30),(9,28),(12,26),(15,24),(18,22),(21,20),(24,18),(27,16),(30,14),(33,12),(36,10),(39,8),(42,6),(45,4),(48,2),(51,0)}
Since z > x+y; z > y > x
(y,z) = {(0,34),(3,32),(6,30),(9,28),(12,26),(15,24),(18,22)}
Since x = 49 - y - z < y
49 - z < 2y
y > (49-z)/2
(y,z) = {(12,26),(15,24),(18,22)}
Since z> x+y = 49-y-z + y = 49 - z
2z > 49
z > 49/2 = 24.5
(y,z) = (12,26)
x = 49 - y - z = 49 - 12 -26 = 49 - 38 = 11
x = 11; y = 12; z = 26
z - x = 26 - 11 = 15
IMO A