Answer:
300,000
Explanation:
Rounding so that a number only has 1 nonzero digit means that you should round to the nearest hundred. Remember when rounding look to the digit to the right of where you are rounding to, if that is 4 or less round down and if it is 5 or greater round up. So to round 511 look at the tens place, since it is less than 4 it rounds to 500. To round 637 look at the tens place, since it is also less than 4 round down to 600. Then to multiply 500 x 600 just multiply the first digits, 5 x 6=30, then add the zeros. In total there were 4 zeros in the estimated equation so the final answer would be 300 plus four zeros.
So 500 x 600=300,000