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

Question

anonymous · Answer

We know that five numbers, (x+y+v+z+w)/5 = 13, and that four numbers, (x+y+v+z)/4 = 10. If we say that x+y+v+z = a, then we have two solveable equations, wouldn't you say?

anonymous · Answer

is it 25..

tbnrfrags · Answer

yeah im failing this class so i couldnt tell you haha

anonymous · Answer

You just have to solve for a, then sub it into the second equation to find w.
$$\frac{ a }{ 4} = 10.........(1)$$
$$\frac{ a+w }{ 5 }.......(2)$$

anonymous · Answer

Sorry, that second equation should have an = 13 at the end of it

mathmath333 · Answer

$\large\tt \color{black}{take~~the~~five~~numbers~~as~~(x-3a),(x-a)(x),(x+a)(x+3a)}$

cj49 · Answer

avg of 5 @13 =65
avg of 4 @10=40
therefore,65-40=25

cj49 · Answer

5th no is 25

mathmath333 · Answer

nice..

tbnrfrags · Answer

ty all<3