Question #cf87c

1 Answer
Nov 14, 2016

Answer:

Jason is #15#

Explanation:

Let
#color(white)("XXX")J# be Jason's age
#color(white)("XXX")S# be Jason's sister's age
#color(white)("XXX")M# be Jason's mother's age

We are told
[1]#color(white)("XXX")J=S+6#
[2]#color(white)("XXX")M=J+S+15#
[3]#color(white)("XXX")M=39#

Combining [2] and [3], we have
[4]#color(white)("XXX")J+S+15=39#

Using [1], we can substitute #S+6# for #J# in [4]
[5]#color(white)("XXX")S+6+S+15=39#

Simplifying
[6]#color(white)("XXX")2S+21=39#

[7]#color(white)("XXX")2S=18#

[8]#color(white)("XXX")S=9#

Using [8], we can substituting #9# for #S# in [1]
[9]#color(white)("XXX")J=9+6 =15#