My father is four times as old as me. In 20 years, he will be only twice as old as me How is my father and how old am l?

3 Answers
Nov 16, 2016

I got that you are #10# years old while your father is #40# years old.

Explanation:

Let us call the age of your father #x# and your's #y#; we can write:
#x=4y#
#x+20=2(y+20)#

we have, substituting the first into the second:
#4y+20=2y+40#
#2y=20#
#y=20/2=10#
so that:
#x=4*10=40#

Nov 16, 2016

I am currently 10 years old and my father is currently 40 years old.

Explanation:

Let's let my age be #m#.

So right now my father's age, Let's call it #n# is #4m# or

#n = 4m#.

So in 20 years I will be #m + 20# years old and my father will be #n + 20# years old. But at this time he will be only twice as old as me. So we can right an equation for our age in 20 years as:

#n + 20 = 2(m + 20)#

Substituting #4m# from the first equation for #n# in the second equation and solving for #m# while keeping the equation balanced gives:

#4m + 20 = 2(m + 20#

#4m + 20 = 2m + 40#

#4m + 20 - 2m - 20 = 2m + 40 - 2m - 20#

#2m = 20#

#(2m)/2 = 20/2#

#m = 10#

So my age is currently 10 years old.

Substituting 10 for #m# is the first equation gives:

#n = 4 * 10#

#n = 40#

Nov 16, 2016

I am 10 years old now and and my father is 40.

Explanation:

Although we are dealing with the ages of two people, we only need to use one variable, because we know how their ages are connected.

Let my present age be #x," "# then my father's age is #4x#

In 20 years time
My age will be #x+20# and my father's age will be #4x +20#

Then, twice my age will be the same as my father's age.

"2 x younger age = older age"
Do not make the mistake of doubling the father's age!

#2xx(x+20) = 4x+20#

#2x+40 = 4x +20#

#40-20 = 4x-2x" "larr# keeping x positive

#20 = 2x#

#10= x#