2/3 is the simplified form of 18/27
Yes you have the correct one good job.
We know that 1 million has 6 zeros. This means 1 million has 7 place values: one for the 1 and 6 for the zeros.
50 has 1 more place value than one, so 50 million has 1 more place value than 1 million.
So, 50 million has 8 place values.
