Tom has ∆ marbles. Bob has 10 marbles. Tom has 3 more marbles the Bob. Which number sentence is correct?

∆ + 3 = 10

∆ - 3 = 10

3 + ∆ = 10

None of these

Tom has 3 more marbles than Bob.

Bob has 10 marbles, so Tom has 10 + 3 = 13 marbles.

So the correct equation is:

∆ - 3 = 10 (Because if Tom has ∆ marbles, and we subtract 3, it equals Bob's 10 marbles.)