Long multiplication and short division

Long multiplication is two easy multiplications

$34\times26$ splits into $34\times6$ and $34\times20$, then you add. The second row ends in a $0$ because you are multiplying by twenty, not by two. Forgetting that zero is the single most common error in the whole method.

The grid method as a check

$34\times26 = (30+4)\times(20+6) = 600+180+80+24 = 884$. Four small products, all easy. If the column method and the grid method disagree, one of them has a slip — and you now know to look.

Short division with a decimal answer

$97\div4$: $9\div4=2$ r $1$, then $17\div4=4$ r $1$. Instead of stopping at “$24$ r $1$”, write a decimal point and a zero: $10\div4=2$, giving $24{,}25$. Which form you give depends on the question.