Question

What is the 20th digit in the decimal expansion for the sum of 2/9 and 1/7

Answer 1

6

Explanation:

Aops question

We have $\frac29 + \frac17 = \frac{14}{63} + \frac{9}{63} = \frac{23}{63}$. Expressing $\frac{23}{63}$ as a decimal using long division, we find $\frac{23}{63}=0.\overline{365079}$. Therefore, every 6th digit after the decimal point is a 9. So, the 18th digit is a 9; the 20th digit is 2 decimal places later, so it is a $\boxed{6}$.

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Answer 2

The 20th digit is 6.

Explanation:

1. Add 2/9 and 1/7.

2/9 + 1/7 = 23/63

2. Convert to a decimal.

23 ÷ 63 = 0.365079...

If you continue to divide, you will notice that the number repeat. So, the decimal would be 0.365079365079...

3. Find the 20th digit.

0.365079365079365079365079