please explain how u worked it out thanks
2007-11-02 03:22:15 · 6 answers · asked by Anonymous in Science & Mathematics ➔ Mathematics
21
17x5 = 85
16x4 = 64
85-64 = 21
2007-11-02 03:26:18 · answer #1 · answered by Anonymous · 1⤊ 0⤋
You know how to calculate the average of five numbers, right? Add them up and divide by the number of addends. Use that to express the facts of the question mathematically.
"the average of 5 numbers is 17" :
(x₁+x₂+x₃+x₄+x₅)/5 = 17
"The average of the first 4 of them is 16":
(x₁+x₂+x₃+x₄)/4 = 16
Multiply both sides by the number of addends:
(x₁+x₂+x₃+x₄+x₅) = 85
and
(x₁+x₂+x₃+x₄) = 64
Subtract the second equation from the first equation:
x₁+x₂+x₃+x₄+x₅ = 85
-1(x₁+x₂+x₃+x₄ = 64)
--------------------------
x₅ =21
2007-11-02 03:45:40 · answer #2 · answered by DWRead 7 · 0⤊ 0⤋
x/4 = 16 Average of four numbers
x+y/5 = 17 Average of five numbers
Solve by substitution:
Solve for x using the first equation:
x/4 = 16
Multiply both sides of the equation by 4:
x = 64
Substitute the value of x in the second equation:
x+y/5 = 17
64 + y / 5 = 17
Multiply both sides of the equation by 5:
64 + y = 85
Subtract 64 to both sides of the equation:
y = 21
2007-11-02 03:51:34 · answer #3 · answered by edith p 3 · 0⤊ 0⤋
(16*4)+x=17*5, so x=21
2007-11-02 03:30:51 · answer #4 · answered by cpinatsi 7 · 1⤊ 0⤋
21
5 x 17 is the total of all the numbers so that makes 85
4x16 is the total of the first 4 makes 64
Therefore the last one is 85-64 = 21
Easy peasy!
2007-11-02 03:28:34 · answer #5 · answered by The Queen 1 · 0⤊ 0⤋
(x1+x2+x3+x4+x5)/5=17
x1+x2+x3+x4+x5=85
(x1+x2+x3+x4)/4=16
x1+x2+x3+x4=64
so x5=85-64=21
2007-11-02 03:40:03 · answer #6 · answered by cidyah 7 · 0⤊ 0⤋