If the mean heart rate of 7 people people is 65 BPM what would an 8th persons heart rate need to be to lower the mean resting heart rate to 63 BPM?

Question

Here it is, I know the answer is 49! (I found it by trial and error!) I just need to know how I can show this in Working!

Thanks, Alex

score 1 · Answer 1 · answered Nov 10 '13 at 05:22

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Dan's answer, without letters & subscripts:

The 7 people have numbers adding up to $7\times65$. The 8 people have numbers adding up to $8\times63$. So the eighth person must have $8\times63-7\times65$.

answered Nov 10 '13 at 05:22

Gerry Myerson

179,216

score 0 · Answer 2 · answered Nov 10 '13 at 05:20

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Start with two equations: $$ \begin{align} \frac{a_1 + a_2 + \ldots + a_7}{7} &= 65 \\ \frac{a_1 + a_2 + \ldots + a_7 + a_8}{8} &= 63. \end{align} $$ Now multiply the first one by $7$, the second one by $8$, and subtract. You get $a_8 = 8 \cdot 63 - 7 \cdot 65 = 49$.

answered Nov 10 '13 at 05:20

Dan Shved

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The standard way to thank someone here is to vote the answer up (if you have enough points to vote) and/or to "accept" the answer by clicking in the check mark next to it. But I'm not trying to rush you, it's fine if you want to wait to see whether even better answers come along. – Gerry Myerson Nov 10 '13 at 05:52

If the mean heart rate of 7 people people is 65 BPM what would an 8th persons heart rate need to be to lower the mean resting heart rate to 63 BPM?

2 Answers2