Which Symbol? printable sheet

Use $+ , -, \times , \div$ and $=$ .

For example:

$2$ ⬜ $3 = 6$

is

$2\times 3 = 6$

and 

$3$ ⬜ $5 - 2$

is

$3 = 5 - 2$

$16$ ⬜ $18 = 34$

$47$ ⬜ $28 = 19$

$18$ ⬜ $2 = 9$

$30$ ⬜ $10\times3$

All of the number sentences below, except two, have two solutions.
Can you find the symbols to use?

$51$ ⬜ $36$ ⬜ $15$

$45$ ⬜ $5$ ⬜ $9$

$27$ ⬜ $36$ ⬜ $63$

$70$ ⬜ $14$ ⬜ $56$

$7$ ⬜ $5$ ⬜ $35$

$50$ ⬜ $5$ ⬜ $10$

Which two number sentences have only one answer?
Can you see why?