Answer:-
- Age of Amy's younger sister=1year
☆Amy is 9 years older than her younger sister.
[tex]\\ \sf\longmapsto Age\:of\:Amy=1+9=10years[/tex]
Let after x years Amy will be 4times old as her sister.
ATQ
[tex]\\ \sf\longmapsto \dfrac{1+x}{9+x}=\dfrac{1}{4}[/tex]
- Using cross multiplication
[tex]\\ \sf\longmapsto 4(1+x)=1(9+x)[/tex]
[tex]\\ \sf\longmapsto 4+4x=9+x[/tex]
[tex]\\ \sf\longmapsto 4x-x=9-4[/tex]
[tex]\\ \sf\longmapsto 3x=5[/tex]
[tex]\\ \sf\longmapsto x=\dfrac{5}{3}[/tex]
[tex]\\ \sf\longmapsto x=1.6[/tex]
[tex]\\ \sf\longmapsto x=2(approx)[/tex]
