Percentuale Inversa

Impara

Trovare il valore originale prima dell'applicazione di una variazione percentuale.

Reverse percentage problems ask you to work backwards from a final value to find the original. If something increased by X%, the final value equals the original times (1 + X/100). To find the original, divide the final value by this multiplier. This is trickier than forward percentages because you can't simply subtract the percentage.

If Final = Original × (1 + X/100), then Original = Final ÷ (1 + X/100)

• After a 20% increase, a price is $120. Original = $120 ÷ 1.20 = $100
• After a 25% discount, a price is $60. Original = $60 ÷ 0.75 = $80
• After a 10% raise, salary is $55,000. Original = $55,000 ÷ 1.10 = $50,000

Come riconoscerlo

• You're given the final value after a percentage change
• You need to find what the value was before the change
• Keywords: 'original price', 'was before', 'started at'

Errori comuni

• Subtracting the percentage from the final (e.g., $120 - 20% = $96, wrong!)
• Using the wrong multiplier (1.20 for increase, 0.80 for 20% decrease)
• Confusing increase (multiply by >1) with decrease (multiply by <1)

Indicazioni per la pratica

Ragionamento Numerico