Multiply the number times itself. For instance. Consider the number 7. Multiply 7 times 7 to get 49.
Round your product from step one to the nearest tens place if the product is two digits. In this example, you would round 49 to 50. If the ones digit is 5 or greater, round to the next highest tens place. If the ones digit is 4 or less, round down.
Multiply the rounded number from step two times the number that you're cubing. In this case, you would multiply 7 times 50. Ignore the zero at first and simply multiply 7 times 5 to get 35. Then add the zero to the ones position to get an approximated answer of 350.
Round the two digit number to the nearest tens place. For example, if you have the number 82, round it to 80.
Ignore the zero in the number for now and multiply the tens digit times itself. In this case, you would multiply 8 times 8 to get 64.
Round your answer from step two to the nearest tens place and multiply it by the same tens digit that you used in step two. In this case you would round 64 to 60. Then you would multiply 60 times 8 to get 480 (multiply the tens digit times the single digit and then add the zero).
Add three zeros to the end of your answer from step three. In this example, you would add three zeros to 480 to get an approximated final answer of 480,000.