Decimals & Percents · Percent in the real world · 7.3

Tax & tip.

Tax and tip are a percent added on. Find the extra (percent of the bill), then add it. 8% tax on $50: 0.08 × 50 = $4 → $54. Or multiply by (100% + the rate).

01 / THE IDEA

See it work.

Watch the method

Tax & tip

8% tax on $50 → $54.

1 / 2
$50 , 8%\$50 \text{ , } 8\%
1

Find the extra

8% of $50 = $4.00.

8%×50=4.008\% \times 50 = 4.00
2

Add it on

Total = original + extra.

=$54.00= \$54.00
02 / YOUR TURN

Practice until it feels automatic.

Your turn

Work it out.

Type dollars, e.g. 12.50.

streak 0
best 0
… =$
— / WHY IT WORKS

The idea underneath.

Onto the bill

Compute the added amount and add it, or multiply by (100% + the rate).

Why it works

8% on $50 adds $4 → $54.

03 / WORKED EXAMPLES

From easy to tricky.

EX 1easy

Add 15% to a $90 bill. What is the total?

1

Find the extra

15% of $90 = $13.50. 15% × 90 = 13.50

2

Add it on

Total = original + extra. = $103.50

EX 2medium

Add 8% to a $60 bill. What is the total?

1

Find the extra

8% of $60 = $4.80. 8% × 60 = 4.80

2

Add it on

Total = original + extra. = $64.80

EX 3hard

Add 8% to a $160 bill. What is the total?

1

Find the extra

8% of $160 = $12.80. 8% × 160 = 12.80

2

Add it on

Total = original + extra. = $172.80

04 / COMMON TRAPS

Where students slip.

Trap

Forgetting to add it back on.

Fix

Tax and tip are added to the bill.

Trap

Using the wrong base.

Fix

The percent is of the original bill.

05 / QUIZ

Test yourself.

The Test

12 problems across three tiers. Auto-graded on submit. Hints and a full walkthrough on every question. Your work is saved on this device — sign in to keep it across devices.

0/12Answered
How to answerType just the value. Formatting won't trip you up — we ignore spaces, capital letters, commas, and subscript style, so t₁ = 5, d = 3 and t1=5,d=3 both count. For a list of numbers, separate them with commas (e.g. 3, 10, 17).
Core

Core (4)

C1

Add 15% to a $30 bill. What is the total?

Need a hint?
  • Find the percent of the bill.
  • Add it to the bill.
C2

Add 20% to a $40 bill. What is the total?

Need a hint?
  • Find the percent of the bill.
  • Add it to the bill.
C3

Add 5% to a $110 bill. What is the total?

Need a hint?
  • Find the percent of the bill.
  • Add it to the bill.
C4

Add 20% to a $30 bill. What is the total?

Need a hint?
  • Find the percent of the bill.
  • Add it to the bill.
Apply

Apply (4)

A1

Add 5% to a $160 bill. What is the total?

Need a hint?
  • Find the percent of the bill.
  • Add it to the bill.
A2

Add 15% to a $90 bill. What is the total?

Need a hint?
  • Find the percent of the bill.
  • Add it to the bill.
A3

Add 5% to a $50 bill. What is the total?

Need a hint?
  • Find the percent of the bill.
  • Add it to the bill.
A4

Add 15% to a $200 bill. What is the total?

Need a hint?
  • Find the percent of the bill.
  • Add it to the bill.
Extension

Extension (4)

E1

Add 5% to a $60 bill. What is the total?

Need a hint?
  • Find the percent of the bill.
  • Add it to the bill.
E2

Add 10% to a $50 bill. What is the total?

Need a hint?
  • Find the percent of the bill.
  • Add it to the bill.
E3

Add 8% to a $130 bill. What is the total?

Need a hint?
  • Find the percent of the bill.
  • Add it to the bill.
E4

Add 10% to a $200 bill. What is the total?

Need a hint?
  • Find the percent of the bill.
  • Add it to the bill.