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9 June, 01:39

Use a ratio box to solve this problem. The cost of a 10-minute call to Boise decreased by 20%. If the cost before the decrease was $3.40, what was the cost after the decrease?

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  1. 9 June, 02:06
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    The cost after the 20% decrease is $2.72

    Step-by-step explanation:

    Here, we are trying to calculate the cost of a 10-minute call before there was a decrease in the amount charged for the call.

    We proceed mathematically as follows,

    To calculate percentage decrease, we can employ the formula;

    (old value - new value) / old value * 100%

    Here our old value or cost was $3.40 and the percentage decrease is 20%

    we plug these values;

    Let the new cost it value be x

    (3.4-x) / 3.4 * 100 = 20

    100 (3.4-x) = 20 * 3.4

    340 - 100x = 68

    100x = 340 - 68

    100x = 272

    x = 272/100

    x = $2.72
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