When writing twenty-one-and-a-half-trillion in scientific notation, what is the exponent needed on the base ten? i also need an explanation on how to find this!

The exponent needed on the base ten is:

Step-by-step explanation:

You should know that the scientific nomenclature that is regularly used to express a trillion is:

But since the base that accompanies base 10 must always be a number less than 10, you cannot use 21.5 (which would be the ideal) but it must be the number with the decimal sign moved once to the left: 2.15 (the which is less than 10), since the decimal sign has been moved to the left in the base, you must increase the exponent by 1 for each digit that you ran the decimal sign, as in this case the sign moved only one digit, you must increase by one the exponent, therefore the exponent will no longer be 9 but 10.

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step-by-step explanation: