I am four times as old as my son, 20 years from now i will be twice as old as my son. How old are we today ?
Answers
Answer:
Let’s say y is your age and d is your daughter’s age
y=4d
That’s the first thing we’re given
20+y=2(20+d)
That one is more complicated, we have to add 20 to both ages… and the second age needs to be doubled AFTER we add the 20, thus the parentheses.
Those are the givens
Substitute the new value for y into the second equation
20+4d=40+2d
Subtract 2d from both sides, subtract 20 from both sides
2d=20
Divide both sides by 2
d=10
Substitute new value for d into y=4d
y=4(10)
y=40
You are 40 and your daughter is 10
Checking our work
40 is 4 times as old as 10, check
In twenty years you will be 60 and she will be 30
60 is twice as old as 30, check
Answer:
Answer:
Let’s say y is your age and d is your daughter’s age
y=4d
That’s the first thing we’re given
20+y=2(20+d)
That one is more complicated, we have to add 20 to both ages… and the second age needs to be doubled AFTER we add the 20, thus the parentheses.
Those are the givens
Substitute the new value for y into the second equation
20+4d=40+2d
Subtract 2d from both sides, subtract 20 from both sides
2d=20
Divide both sides by 2
d=10
Substitute new value for d into y=4d
y=4(10)
y=40
You are 40 and your daughter is 10
Checking our work
40 is 4 times as old as 10, check
In twenty years you will be 60 and she will be 30
60 is twice as old as 30, check