Explanation
Now, $$a>b$$
$$=>\dfrac{a}{b}>1$$
$$\therefore \dfrac{a}{b}>\dfrac{a+1}{b+1}$$ and
$$\dfrac{a-1}{b-1}>\dfrac{a}{b}$$
Thus, $$\dfrac{a-1}{b-1}>\dfrac{a+1}{b+1}$$
let the number of boys and girls in the college be 7x and 8x
their increased number is (120% of 7x) =
$$\Rightarrow \frac{120}{100}\times 7x$$
$$\Rightarrow \frac{42x}{5}$$
And (10% of 8x).=$$\Rightarrow \frac{110}{100}\times 8x$$
$$\Rightarrow \frac{44x}{5}$$
$$\therefore $$Required Ratio=$$\frac{42x}{5}:\frac{44x}{5}$$
$$21:22$$
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