The number of pounds of one-dollar-a-pound coffee needed to mix with 80 pounds of 70¢ a
pound coffee to make a mixture worth 84¢ a
pound is
(A) 70
(B) 80
(C) 95
(D) 65

The number of pounds of a constituent in a mixture given the cost of the

mixture and the cost and mass of the other constituent can be calculated

by using an equation to model the system

The correct option for the number of pounds of one-dollar- pound coffee needed is option A

(A) 70 pounds

The procedure for arriving at the correct option is as follows:

The given parameters are;

The cost of the the coffee for which the mass in the mixture is to be determined = One-Dollar a pound = 100 ¢ a pound

The mass of the coffee 70¢ a pound coffee to be mixed = 80 pounds

The cost per pound of the mixture = 84 ¢ a pound

The required parameter;

The number of pounds of the one-dollar-a-pound (100 ¢ a pound) coffee in the mixture

Method:

Let x (pound) represent the number of pounds of the one-dollar-a-pound coffee in the mixture, we have;

Mass of mixture = Mass of the one-dollar-a-pound in the mixture, x + Mass of 70 ¢ a pound in the mixture, 80

∴ Mass of mixture in pounds = x + 80

Cost = Cost per pound × Number of pound

Find solution by applying the equation;

Cost of the constituents = Cost of the mixture

Where;

Cost of the constituents = $1 × x + 70 ¢ × 80 = 100 ¢ × x  + 70 ¢ × 80

Cost of the mixture = 84 ¢ × (x + 80)

Therefore;

100 ¢ × x  + 70 ¢ × 80 = 84 ¢ × (x + 80)

The above can be expressed as 100·x + 70×80 = 84 × (x + 80)

Expanding, evaluating and collecting like terms gives;

100·x + 5,600 = 84·x + 6,720

100·x - 84·x = 6,720 - 5,600 = 1,120

16·x = 1,120

x = 1,120/16 = 70

The number of pounds of one-dollar- pound coffee needed, x = 70 pounds

Learn more about equation modelling here;

A

Step-by-step explanation:

Let's say we need x pounds of one-dollar-a-pound coffee . The coffee must average out to 84 cents a pound, and the formula for average is

sum of cost of coffee / number of pounds of coffee, so we have

0.84 = total cost of coffee / (x+80) . The total cost of coffee can be found to be the sum of the cost of $1 coffee and 70 cent coffee, so we have

0.84 = (cost of $1 coffee + cost of 70 cent coffee) / (x+80)

The cost of $1 coffee can be found by adding $1 for each pound of one dollar coffee, or $1 * x. Similarly, the cost of 70 cent coffee is equal to 0.70 * 80, so we have

0.84 = (1*x+0.7*80)/(x+80)

0.84 = (x+56)/(x+80)

multiply both sides by (x+80) to remove a denominator

0.84(x+80) = x+56

0.84x + 67.2 = x+56

subtract both sides by 56 and 0.84x to isolate the x and its coefficients

11.2 = 0.16 x

divide both sides by 0.16 to isolate x

11.2/0.16 = x = 70

answer: f true

step-by-step explanation: