Mrs Lu is 29 years old. Her son is 5 years old. In how many years' time will she be 4 times as old as her son?
2007-02-06 19:20:40 · 6 answers · asked by bio-nana121 3 in Science & Mathematics ➔ Mathematics
No algebra/substitution methods are allowed.
2007-02-06 23:47:27 · update #1
No algebra/ substitution methods are allowed.
2007-02-06 23:48:00 · update #2
Age now -
Mrs Lu: 29
Son: 5
Age in x years:
Mrs Lu: 29 + x
Son: 5 + x
We want to know in how many years Mrs Lu is 4 times as old as her son; that is, we want to know when
29 + x = 4(5 + x)
Expand the right hand side,
29 + x = 20 + 4x
Simplify
-3x = -9
x = 3
Therefore, in 3 years, she will be 4 times as old as her son.
It makes sense too, because in 3 years, she will be 32 years old, and her son will be 8.
2007-02-06 19:30:13 · answer #1 · answered by Puggy 7 · 2⤊ 0⤋
Let x be the number of years.
Then her age will be 29 + x, and her son's age will be 5 + x. So we want
29 + x = 4(5 + x)
=> 29 + x = 20 + 4x
=> 29 - 20 = 4x - x
=> 9 = 3x
=> x = 3.
So this will happen in 3 years' time, when she is 32 and her son is 8.
2007-02-06 19:28:59 · answer #2 · answered by Scarlet Manuka 7 · 1⤊ 0⤋
a
(29 + x) = 4*(5+x)
29 + x = 20 + 4x
9 = 3x
x = 3
in 3 years Mrs Lu will be 32 ... her son will be 8
8 * 4 = 32
2007-02-06 19:27:59 · answer #3 · answered by atheistforthebirthofjesus 6 · 1⤊ 0⤋
In 3 years time, her son wil be 8 and she will be 32, which is 4 times older.
2007-02-06 19:29:48 · answer #4 · answered by ScienceBug 1 · 0⤊ 1⤋
let us say In x years' time
29+x=4(5+x)
29+x=20+4x
29-20=4x-x
9=3x
x=9/3
x=3 years
2007-02-06 19:30:11 · answer #5 · answered by iyiogrenci 6 · 1⤊ 0⤋
set up this equation:
49 + x = 20 + 4x
Solve: and you get 29/3
presto!
oops: she's 29
2007-02-06 19:31:23 · answer #6 · answered by Jian C 3 · 0⤊ 1⤋