What method were you taught in 5th grade?

without knowing this, here are some methods that could be used:

Long multiplication: This is the standard method that most people learn in school. It involves breaking down the problem into smaller multiplication problems and then adding up the results. This method can be time-consuming and is not the fastest.

Splitting and combining: This method involves splitting one or both of the numbers being multiplied into parts that are easier to multiply mentally, and then combining the results. For example, to multiply 36 by 24, you could split 24 into 20 and 4, and then multiply 36 by 20 (720) and 36 by 4 (144), and then add the results (864).

Doubling and halving: This method involves doubling one number and halving the other, and then using those results to simplify the multiplication problem. For example, to multiply 28 by 16, you could double 16 to get 32 and halve 28 to get 14, and then multiply 14 by 32 (448).

Using number properties: This method involves using properties of numbers, such as distributivity, to simplify the multiplication problem. For example, to multiply 34 by 12, you could distribute the 12 as (30 + 4) and then multiply 34 by 30 (1020) and 34 by 4 (136), and then add the results (1156).

In terms of speed, the fastest method will depend on the specific numbers being multiplied and the person doing the mental calculation. Some people may find certain methods easier or more intuitive than others, so it's a good idea to practice and experiment with different methods to see what works best for you.
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