multiplication

[murali0298]

how do you multiply by 131? Like 422 * 131..
I don't know the trick for this

[nsguy1350]

Yes!!! You finally joined! Now get everyone else on here too so I can answer the questions you guys have.

Alright, I taught this the day you couldn't come, a couple of weeks ago. This is 3-digit multiplication, and there is no specific 131 or 422 trick. Here's what you do:

This is basically LOIF, except you treat a three-digit number as a two digit number by making the last two digits function as one.
Multiply the last two digits of each number. Write the last two digits of this number, and carry if necessary. (31 x 22)
Multiply the last two digits of the first number by the first digit of the second number, then multiply the first digit of the first number by the last two of the second. Add these results. (4 x 31 + 1 x 22 + carried digits).
Multiply the first two digits of the numbers, add any carried digits, then write the number.

131 x 422.
22 x 31 = 22 x 30 + 22 = 682. Write 82, carry 6.
4 x 31 + 1 x 22 + 6 = 152. Write 52, carry 1.
4 x 1 + 1 = 5. Write 5.
Final answer should be 55282.

213 x 411.
13 x 11 = 143. Write 43, carry 1.
2 x 11 + 4 x 13 + 1 = 75. Write 75.
2 x 4 = 8. Write 8.
Final answer should be 87543.

Practice and you'll get used to this. Also, try to group your questions into one post at a time.