SOLUTION: To make an A in a class, Colin must have at least an average of 94. On the first three tests he has an average of 91. What must he average on the last three tests to have an aver

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Write down what you know.
1. Colin's average from first three tests.
2. Colin's average from first three and last three tests must equal at least 94.
3. Here's the unknown you need to find. It's Colin's average for the last three tests. Call it x.
From equation 1,

Multiply both sides by 3.
4.
From equation 2,

Multiply both sides by 6.
5.
From equation 4, you know that

Substitute that into equation 5.


Use the additive inverse of 273.

If I divide both sides by 3, I'll get an equation that looks like equation (3).



Colin better start studying. He needs a 97 average on his last three tests to average 94.