In a group 120 children there are teice as many boys as girls. How many girls are there?
2 answers:
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Given
we have
Squaring both sides, we have
And finally
Note that, when we square both sides, we have to assume that
because we're assuming that this fraction equals a square root, which is positive.
So, if that fraction is positive you'll actually have roots: choose
and you'll have
Which is a valid solution. If, instead, the fraction is negative, you'll have extraneous roots: choose
and you'll have
Squaring both sides (and here's the mistake!!) you'd have
which is not a solution for the equation, if we plug it in we have
Which is clearly false
Answer:
8 and 12
Step-by-step explanation:
Sides on one side of the angle bisector are proportional to those on the other side. In the attached figure, that means
AC/AB = CD/BD = 2/3
The perimeter is the sum of the side lengths, so is ...
25 = AB + BC + AC
25 = AB + 5 + (2/3)AB . . . . . . substituting AC = 2/3·AB. BC = 2+3 = 5.
20 = 5/3·AB
12 = AB
AC = 2/3·12 = 8
_____
<em>Alternate solution</em>
The sum of ratio units is 2+3 = 5, so each one must stand for 25/5 = 5 units of length.
That is, the total of lengths on one side of the angle bisector (AC+CD) is 2·5 = 10 units, and the total of lengths on the other side (AB+BD) is 3·5 = 15 units. Since 2 of the 10 units are in the segment being divided (CD), the other 8 must be in that side of the triangle (AC).
Likewise, 3 of the 15 units are in the segment being divided (BD), so the other 12 units are in that side of the triangle (AB).
The remaining sides of the triangle are AB=12 and AC=8.
