+870 A teacher tells one of his students :
«I am four times as old as you were,
when I was as old as you are.»
The teacher is 40 years old; how old is the student ?
+129852 This is a good one !!!!
Let the student's age be x.......let the years that have elapsed since the teacher was the student's current age = y....so....
40 - y = x → x + y = 40 (1)
and
4(x - y) = 40 → x - y = 10 (2)
Add equations 1 and 2
2x = 50 divide both sides by 2
x = 25 and that's the student's age now
And x + y = 40 so 25 + y = 40 so y = 15 years have elapsed since the teacher was the same age as the student is now
Proof
15 years ago, the student was 10......and the teacher was 25, the same age as the student is now
And the teacher is now 4 times as old as the student was then
+129852 This is a good one !!!!
Let the student's age be x.......let the years that have elapsed since the teacher was the student's current age = y....so....
40 - y = x → x + y = 40 (1)
and
4(x - y) = 40 → x - y = 10 (2)
Add equations 1 and 2
2x = 50 divide both sides by 2
x = 25 and that's the student's age now
And x + y = 40 so 25 + y = 40 so y = 15 years have elapsed since the teacher was the same age as the student is now
Proof
15 years ago, the student was 10......and the teacher was 25, the same age as the student is now
And the teacher is now 4 times as old as the student was then
+870 I checked the answer in my book, and you're right. You deserved 20/20 and a brownie :
Congratulations 
