father age is 4 times that of his son 5 years back it was 7 times his age now is
Answers
Answer:
10
Step-by-step explanation:
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Answer:
The son is 10 yo. and the father is 40 yo.
Explanation:
So the father's age (F) is 4 times the son's age (S).
F
=
4
×
S
5 years ago, the father's age (
F
−
5
) was 7 times that of his son 5 years ago (
S
−
5
).
F
−
5
=
7
×
(
S
−
5
)
So:
F
=
7
×
(
S
−
5
)
+
5
←
adding 5 to both sides
Now we can take the first equation and set it equal to the second, since both "right" sides are equal to F.
7
×
(
S
−
5
)
+
5
=
4
×
S
Now we solve for S:
7
×
S
−
7
×
5
+
5
=
4
×
S
←
distributing the 7
7
×
S
−
35
+
5
=
4
×
S
←
finishing the multiplication
7
×
S
−
30
=
4
×
S
←
adding
−
30
and
5
7
×
S
=
4
×
S
+
30
←
adding 30 to both sides
7
×
S
−
4
×
S
=
30
←
subtracting
4
×
S
from both sides
3
×
S
=
30
←
subtracting
4
×
S
from
7
×
S
S
=
30
3
←
dividing both sides by 3
S
=
10
So, the son's current age is 10 years old and the fathers is 4 times that, or 40 years old.
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