| Present ages of X and Y are in the ratio 3: 5 respectively. Eight years hence this ratio will be 5: 7. What is the Ys present age? |
A) 20
B) 21
C) 22
D) 23
Correct Answer: A
Solution :
| Let present age of X be x yr and present age of Y be y yr. |
| Then, \[\frac{x}{y}=\frac{3}{5}\]\[\Rightarrow \]\[5x=3y\]\[\Rightarrow \]\[\frac{x+8}{y+8}=\frac{5}{7}\] |
| \[\Rightarrow \] \[7x+56=5y+40\] |
| \[\Rightarrow \] \[7x-5y=-16\] |
| \[\Rightarrow \] \[7\left( \frac{3y}{5} \right)-5y=-16\] |
| \[\Rightarrow \] \[21y-25y=-\,80\] |
| \[\Rightarrow \] \[-\,4y=-\,80\]\[\Rightarrow \]\[y=20yr\] |
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