Lizzy: George donated half his monthly income to charity and spent $20 from the other half on groceries. If he now has $100 left, how much was his monthly income?.
Me: Hmmm, let me think. I think this is the detailed solution:
Half his monthly income is $100 + $20 = $120. His monthly income therefore is 2 * $120 = $240. Final answer: 240.