1000 x 10 = 10000
1000 times 10 is 10000. Multiplying by ten adds one zero, so the three zeros in 1000 become four. The answer is ten thousand, written as a 1 with four zeros.
1,000 × 10 = 10,000
Adding 1,000 to itself 10 times gives the same answer.
Why 1000 x 10 is 10000
1000 x 10 = 10000. Multiplying by ten never changes a digit. It only moves the whole number one place to the left, which in practice means writing one more zero. 1000 already carries three, and the 10 adds the fourth.
The same total as 100 x 100
10000 is a square number, so 100 x 100 reaches exactly the same answer: 100 multiplied by itself is 10000. Two sums that look nothing alike, one total. Ten thousand also had its own word in Greek, a myriad, which is where the English word comes from.
Where ten thousand is the unit
Finance counts in ten thousandths. One basis point is one hundredth of one percent, so 10000 basis points make a whole. That is why interest rate moves are quoted the way they are.
One zero away
The common slip is 100 x 1000, which is 100000, one hundred thousand. Five zeros, not four. If the answer is meant to be ten thousand, only four zeros follow the 1. The multiplication answers index has the rest.