To find how much the U.S. national debt increased from 1971 to 2021, we need to subtract the debt in 1971 from the debt in 2021.
The debt in 2021 is: \[ 2.9617 \times 10^{13} \]
The debt in 1971 is: \[ 3.98 \times 10^{11} \]
First, we need to express both numbers in the same power of ten. We can convert \( 3.98 \times 10^{11} \) to the same power of ten as \( 2.9617 \times 10^{13} \):
\[ 3.98 \times 10^{11} = 0.0398 \times 10^{13} \]
Now we can subtract:
\[ 2.9617 \times 10^{13} - 0.0398 \times 10^{13} = (2.9617 - 0.0398) \times 10^{13} = 2.9219 \times 10^{13} \]
Therefore, the increase in the national debt over the 50-year period from 1971 to 2021 is:
\[ 2.9219 \times 10^{13} \]
The correct answer is: \[ \boxed{2.9219 \times 10^{13}} \]
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