How many pounds of gourmet candy selling for $2.20 per pound should be mixed with 6 pounds of gourmet candy selling for $1.20 per pound to obtain a mixture selling for $1.60 per pound?

1 Answer
Feb 5, 2016

color(green)("$1.20 candy amount is "6"lb"$1.20 candy amount is 6lb
color(green)("$2.20 candy amount is "4"lb"$2.20 candy amount is 4lb

Explanation:

Tony B

There are two ways of solving this.
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color(blue)("Method 1")Method 1

color(Brown)("Straight line graph approach")Straight line graph approach

Standard form equation" "->y=mx+c y=mx+c

In this case:" "c=1.2"; "m=(2.20-1.20)/100 = 1/100"; "y=1.60 c=1.2; m=2.201.20100=1100; y=1.60

1.6=x/100+1.21.6=x100+1.2

x=(1.6-1.2)xx100" "color(purple)(-> x=0.4xx100)x=(1.61.2)×100 x=0.4×100

x=40-> 40%x=4040%
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color(blue)("Method 2")Method 2

color(Brown)("Ratios, which is the same thing as method 1 just that this fact is in disguise.")Ratios, which is the same thing as method 1 just that this fact is in disguise.

The approach is based on the principle that the gradient is constant.

100/(2.2-1.2)=x/(1.6-1.2)1002.21.2=x1.61.2

Basically this is saying that the gradient of the whole is the same gradient as part of it!

100/1=x/0.41001=x0.4

color(purple)(0.4xx100=x)0.4×100=x

x=40" " -> 40%x=40 40%

color(green)('"NOTE THAT IS 40% OF THE $2.20 CANDY")
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color(blue)("Determine the weights of each constituent")

so 100%-40% =60% as the proportion of the $1.20 candy

Let the whole weight be w then

60/100 w=6

w=(6xx100)/60" "=" "100/10" "=" "10lb

So

color(green)("$1.20 candy amount is "6"lb"
color(green)("$2.20 candy amount is "10-6 = 4"lb"