Try it! Suppose the number I'm thinking of is 49.
The product of 49 and 7 is 343; we subtract 3 from that, obtaining 340.
Divide this 340 by 13: 340/13.
Double this quotient: 680/13
680 + 390
Add 30 to this result: 680/13 + 30 = ------------------ = 1070/13
13
Sadly, this is not 50, as we'd hoped.
Why don't you try doing this yourself? Would you do anything differently from the way I did it?
