What is 20% of 13,050,000,000,000,000,000,000

My calculator doesn't work with numbers this big and it doesn't do scientific notation, either <_<

13,050,000,000,000,000,000,000/5
=261,000,000,000,000,000,000,000

First, estimate the answer, it is going to be greater than 10% and less than 50%

Next, omit the decimal point and trailing zeros, and just multiply
2 x 1305.

Now put in the trailing zeros and the decimal point to get a number that is close to your estimate.

One fifth of that. Take that number and truncate the zeroes up leaving 13 050 000 times 0.2, then add the zeroes back on.

Move the decimal to the left twice and multiply by 2.

2.61e+21