The whole is 100%. She spent 60%, so the $20 left is the other 40%.

spent 60%left 40% = $20100% = ?

Plain numbers are given; italic underlined numbers are worked out.

  1. Left → 100% − 60% = 40% → $20
  2. 10% → $20 ÷ 4 = $5
  3. 100% → 10 × $5 = $50

She had $50 at first.

Check: 60% of $50 = $30 spent, $50 − $30 = $20 left. ✓