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# Plugging In: Basic Technique

Basmati rice costs $$(a−b)$$ per kilogram in standard 7 kilogram packages, where $$a\gt b\gt 0$$, and costs $$a$$ per kilogram in nonstandard packages. In terms of $$a$$ and $$b$$, what is the lowest possible price of exactly 24 kilograms of Basmati rice, in dollars?
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That's right. The variables in the question and in the answer choices call for __Plugging In__. Use good numbers such as $$a=5$$ and $$b=3$$. Now the question reads as follows: >{color:purple}Basmati rice costs __$2__ per kilogram in standard 7 kilogram packages and __$5__ per kilogram in nonstandard packages. What is the lowest possible price for 24 kilograms of Basmati rice in dollars?{/color} How does it feel now? Probably much better…. Exactly 24 kilograms are made of 3 standard packages of 7 kilograms, plus 3 kilograms, hence >$$2\times 21 + 5\times 3 = 57$$ Your goal is __\$57__. __Plug In__ $$a=5$$ and $$b=3$$ in the answer choices, and eliminate any answer choice that clearly is not 57. The correct answer is C.
$$24a-3b$$
$$21a-3b$$
$$24a-21b$$
$$21a-21b$$
$$21a-24b$$