かけ算の筆算

Take $243\times 6$. Line up the place values and multiply from the ones. $3\times 6=18$ → write 8, carry 1. $4\times 6=24$, plus the carried 1 is 25 → write 5, carry 2. $2\times 6=12$, plus the carried 2 is 14. The answer is 1458. Always remember to add the carried number to the next column.

For $34\times 27$, split 27 into 20 and 7 and work in two rows. First multiply by the ones, 7: $34\times 7=238$. Then multiply by the tens, 2 (really 20): $34\times 20=680$. Finally add the two rows: $238+680=918$. The second row starts in the tens column, so shift it one place left (or write a 0 in the ones place).

Check that your answer is sensible by estimating. For $34\times 27$, round 34 to 30 and 27 to 30: $30\times 30=900$. The real answer, 918, is close to 900, so it looks right. If you had got 90 or 9000, that would be a sign you slipped a digit.