Question 1186104
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You can get come good mental exercise by solving the problem using logical analysis and a bit of mental arithmetic.<br>
(1) A year ago, the mother's age was twice Sally's age, so the mother's age was an even number.  So now the mother's age must be an odd number.<br>
(2) Since a year ago the mother's age was twice Sally's age, now her age is still very close to twice Sally's age.<br>
So the mother's age is an odd number which is about twice as much as her age with the digits reversed.  Now do some trial and error:<br>
Now 31 and 13; a year ago 30 and 12.  no....
Now 52 and 25; a year ago 51 and 24.  no....
Now 73 and 37; a year ago 72 and 36.  YES!!!<br>
ANSWER: 73 and 37 now<br>
It's also good practice solving the problem using formal algebra, which is what you probably want.  This is not a particularly easy problem for a student just beginning to study algebra....<br>
Let the mother's current age be the 2-digit number "AB" (where AB does NOT indicate multiplication)
Then the daughter's current age is "BA"<br>
Algebraically, then, the mother's age is 10A+B and the daughter's age is 10B+A.  <-- MAKE SURE you understand that; the VALUE of the 2-digit number "AB" is 10A+B<br>
We are told that a year ago the mother's age was twice Sally's age.<br>
Mother's age 1 year ago: 10A+B-1
Sally's age 1 year ago: 10B+A-1<br>
{{{10A+B-1=2(10B+A-1)}}}
{{{10A+B-1=20B+2A-2}}}
{{{8A=19B-1}}}<br>
With the requirement that A and B are both positive single-digit integers, the only solution to that equation is A=7 and B=3.  So their ages are...<br>
ANSWERS:
mother: "AB" = 73
Sally: "BA" = 37<br>