Question

The average (arithmetic mean) of 5 numbers is 13. If the average of 4 of these numbers is 10, what is the fifth number?

Answer 1

Let \(s\) be the sum of the and \(a\) be the fifth number. We know:
\[\frac{s}{4}=10\]\[\frac{s+a}{5}=13\]So you know how to solve for a?

Answer 2

Let \(s\) be the sum of the first four numbers, I meant to type.

Answer 3

7?

Answer 4

Nope. First... what is \(s\)?

Answer 5

Can you solve for \(s\) in the first equation first?

Answer 6

Then plug your result into the second equation.

Answer 7

s is 40

Answer 8

Okay so plug that into the second equation:\[\frac{s+a}{5} = 13 \Rightarrow \frac{(40)+a}{5} = 13\]Now can you solve for \(a\)?

Answer 9

5

Answer 10

\(5 * 13 = 65\text{ and } 65 - 40 = 25\).

Answer 11

Be careful with your math.

Answer 12

so 25 is the answer????

Answer 13

Yeah, do you understand how I got it?

Answer 14

yah. thanls