Bunuel wrote:

aimlockfire1 wrote:

An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% impurity and copper has 58% , what is the avg impurity percentage ?

a) 20%

b) 41.1%

c) 35%

d) 38%

e) 43.1%

(4*0.2 + 5*0.58)/(4+5) = ~41%.

Answer: B.

Tin and copper are in ratio of 4:5. So let total mixture be 4+5 = 9.

So, tin = 4 and copper = 5.

Now, tin has 20% impurity = 20% * 4 = 0.8

Also, copper has 58% impurity = 58% * 5 = 2.9

Average = (0.8 + 2.9)/(4+5)

= 3.7/9

= 0.411

= 41.1%

Hence option (B).

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