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15) Ellie is six years older than Maisy. Zoe istwice as old as Ellie. The sum of their ages is50. How old is Zoe?

Sagot :

EXPLANATION

Assuming that x represents the age of Ellie, y represents the age of Maisy and z represents the age of Zoe, we can apply the following relationships:

x + y + z = 50 (1)

x = 6 + y (2)

z = 2x (3)

We have a system of three equations with three variables, thus we can compute the system as follows:

[tex]\mathrm{Substitute\: }z=2x[/tex][tex]\begin{bmatrix}x=6+y \\ x+y+2x=50\end{bmatrix}[/tex][tex]Simplify\text{ }x+y+2x=50[/tex]

Grouping like terms:

[tex]3x\text{ + y = 50}[/tex]

Now, we have:

[tex]\begin{bmatrix}x=6+y \\ 3x+y=50\end{bmatrix}[/tex][tex]\mathrm{Substitute\: }x=6+y[/tex][tex]\begin{bmatrix}3\mleft(6+y\mright)+y=50\end{bmatrix}[/tex]

Applying the distributive property:

[tex]\begin{bmatrix}18+4y=50\end{bmatrix}[/tex][tex]\mathrm{Subtract\: }18\mathrm{\: from\: both\: sides}[/tex][tex]18+4y-18=50-18[/tex][tex]Simplify\colon[/tex][tex]4y=32[/tex][tex]\mathrm{Divide\: both\: sides\: by\: }4[/tex][tex]\frac{4y}{4}=\frac{32}{4}[/tex][tex]Simplify\colon[/tex][tex]y=8[/tex][tex]\mathrm{For\: }x=6+y[/tex][tex]\mathrm{Substitute\: }y=8[/tex][tex]x=6+8[/tex][tex]Simplify\colon[/tex][tex]x=14[/tex][tex]\mathrm{For\: }z=2x[/tex][tex]\mathrm{Substitute\: }x=14,\: y=8[/tex][tex]z=2\cdot\: 14[/tex][tex]\mathrm{Simplify}[/tex][tex]z=28[/tex][tex]\mathrm{The\: solutions\: to\: the\: system\: of\: equations\: are\colon}[/tex][tex]x=14,\: z=28,\: y=8[/tex]

In conclusion, the age of Zoe is 28 years old.