Question Video: Evaluating Algebraic Expressions Mathematics

Evaluate 7𝑥 + 5 when 𝑥 = 10.

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Video Transcript

Evaluate seven 𝑥 plus five when 𝑥 is equal to 10.

So we’re told that 𝑥 is equal to 10 and wherever we see 𝑥 in our expression, we have to replace that with 10. But we have to think quite carefully. We don’t just literally write 10 because that would then be 710 plus five. Well, that seven 𝑥 means seven times 𝑥. So we have to think about what the expression actually means before we substitute those numbers in. So seven 𝑥 plus five means seven times 𝑥 plus five. So when 𝑥 is 10, that means seven times 10 plus five. Now, if you think about your order of operations, you do multiplication and division before you do addition and subtraction. So we’re going to evaluate this first. Now, seven times 10 is 70. So that’s 70 plus five, which gives us an answer of 75.

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