Multiplication is just shorthand for repeat addition, as such the 2 values are linked together, you can imagine an invisible parenthesis.

1 + 2 x 3
= 1 + (3 + 3) , or 1 + (2 + 2 + 2)
= 7

1 + 5 x 10

The above is similar to saying you are adding $1 to a 5-pack of $10s (or a 10-pack of $5s), which equals $51 and not $60.

If you instead meant to have a 10 packs each containing both a $5 & $1, so $60 total, your expression should be:

(1 + 5) x 10