Write this ratio as a fraction in lowest terms.
$90 to $70
To write this ratio as a fraction in lowest terms, we divide both values by their greatest common divisor.
The greatest common divisor of $90 and $70 is $10 since both can be divided by 10 without a remainder.
Dividing $90 by $10 gives 9 and dividing $70 by $10 gives 7.
Therefore, the ratio of $90 to $70 written as a fraction in lowest terms is $\boxed{\frac{9}{7}}$.