Question

what is the best estimate for this product? 81 x409

Answer 1

81*409=33,129

Answer 2

For estimation do 33,130

Answer 3

80 × 400 = 8 × 4 and then write 3 zeros in front of it.

Answer 4

Or 33,000

Answer 5

No, estimating the numbers you multiply before multiplying. This is silly, but that is how it works .

Answer 6

Like I did, I estimated
81≈80
409≈400

Answer 7

Which way is correct SolomonZelman?

Answer 8

Well, I would not round up the numbers before multiplying, I agree that it is stupid, but that is what they are asking for here -:(

Answer 9

They are teaching a common sense here, that if you would try to multiply 28 and 401, you would say it is about 12,000. Because you would multiply 30 × 400. Even though the exact answer would be 11,228.
This is done, so that people can find what the number can be when they have no calculator or paper.

Answer 10

Thank you! You taught me something really valuable.

Answer 11

Well, I personally would multiply those together or use a calculator on an i-phone. People sometimes use this method, but I am not a fan of it.

What YOU did is better, estimating after multiplying, not before.