Question

What did this person do wrong

Answer 1

They didn't put a 0 for the one's digit after multiplying 335 and 20.

Explanation:

Your multiplication is right.

Let me write out what you did again:

3.35

* 2.9

--------

3015

+6700

------------

9715

So the answer is 9.715 .

Now what could the person have done to get the 3.685?

A common error that some students forget to add is a 0 for the product of 335 and 20.

That is, what do you get when you do:

3015

+670

-------

3685

Then moving the decimal over 3 times gives: 3.685.

So they forgot to add a 0 when moving over to multiply the top digits to the tens digit of the second number.