A jeweler has bars of 18-carat gold and 12- carat gold. How much of each must be melted
together to obtain a bar of 16-carat gold weighing 120 grams? (Pure gold is 24 carat)
Let’s assume the quantity of 18-carat gold as x gm and 12-carat gold as y gm.
Then according to the first condition given in the problem, we have
x + y = 120 … (i)
Pure gold is 24 carat
So, the purity of 18-carat gold = (18/24) x 100%
= (¾) x 100
= 75%
Purity of 12 carat gold = (12/24) x 100%
= ½ x 100%
= 50%
And, the purity of 16-carat gold = (16/24) x 100%
= (2/3) x 100%
= 200/3%
Now, according to the second condition given in the problem, we have
75x + 50y = 200/3 x 120
75x + 50y = 200 x 40
75x + 50y = 8000
3x + 2y = 320 … (ii)
Performing (ii) – 2 x (i), we get
3x + 2y = 320
2x + 2y = 240
(-)—(-)—(-)---
x = 80
On substituting the value of x in equation (i), we get
80 + y = 120
y = 120 – 80
y = 40
Therefore, the jeweler requires 80 gm of 18-carat gold and 40 gm of 12-carat gold to obtain a bar of 16
carat gold weighing 120 gm.
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