Question

which number makes this sentence true? 7.8×3.6×1=7.8×? 1,3.6,4.6,7.8

Answer 1

In the left hand side, you're multiplying 7.8 by $3.6\times 1$

In the right hand side, you're multiplying again 7.8 by a mysterious number.

So, the unknown number must be $3.6\times 1$

Every number remains unchanged when multiplied by 1, so the answer is 3.6