Mathslive.ie

MONEY

Exam Cog
①PERCENTAGES

p% of A = (p/100) × A

Increase: ×(1 + p/100)

Decrease: ×(1 − p/100)

②PROFIT & ERROR

% profit = increase/original × 100

% error = error/real × 100

★ Always divide by the ORIGINAL / real value
③REVERSE %

Price includes a %? It is more than 100%.

110% = 165 → 100% = 165/110 × 100

Profit as money: p% = €X → 1% → 100%

④COMPOUND INTEREST

F = P(1 + i)t

i = rate as a decimal, t = years

Find P: P = F ÷ (1+i)t

⑤LOANS
  1. Add interest for the year (× 1+i)
  2. Subtract any repayment
  3. Repeat for the next year
⑥WATCH-OUTS
⚠ AER/APR is the yearly rate. Subtract a repayment BEFORE charging the next year’s interest.