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Toolbox · Money & shopping

Money & shopping

Price times quantity, discounts, change and a banknote breakdown from ¥100 down to ¥0.1.

Formula

\begin{gathered} S = p \times q,\quad T = S(1-d) \\ C = M - T \end{gathered}

Subtotal = price × quantity; total = subtotal × (1 − discount); change = paid − total.

Unit price · 元QuantityDiscount · %Paid · 元

Enter 10 for a 10% discount and 0 for none; paid 0 skips the change calculation.

Presets

Amount due33.75元

Subtotal37.5

Discount3.75

Change16.25

Subtotal37.5元

Discount3.75元

Amount due33.75元

Change16.25元

Change in notes and coins100×16 + 20×1 + 5×1

Denomination	Count	Subtotal
20 元	1	20
10 元	1	10
1 元	3	3
0.5 元	1	0.5
0.1 元	2	0.2

Steps

4 / 4

1Formula
$S = 12.5 \times 3 = 37.5$
Compute the subtotal first.
2Substitute
$D = 37.5 \times 10\% = 3.75$
Apply the discount rate.
3Solve
$T = 37.5 - 3.75 = 33.75$
Subtotal minus discount is the amount due.
4Conclusion
$C = 50 - 33.75 = 16.25$
Paid minus total is the change.

Concept

Money is written with two decimals; calculations are safest in the smallest unit (cents), where every step is integer arithmetic.

Change is subtraction: paid minus total. Breaking the amount into the largest notes first is how a till works.

Going further

Discounts and tenths: A 20% discount means paying 80% of the price; do not confuse it with taking 8 yuan off.

Common mistakes

Estimate first: 12.5 × 3 is about 37.5, so paying 50 leaves a bit over 10 in change.
Working in cents avoids floating point surprises such as 0.1 + 0.2.

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