Comparison & Replacement — Primary Level

The Story

Kiki buys fruit at the market.

Trip A: 🍎 apples and 🍌 bananas cost a total of Rp T₁.
Trip B: 🍎 apples and 🍌 bananas cost a total of Rp T₂.

By comparing the two trips and replacing items, we can find the price of one apple and one banana.

Trip	Apples	Bananas	Total
A	x₁	y₁	Rp T₁
B	x₂	y₂	Rp T₂

Goal: price of one apple = Rp a, and one banana = Rp b.

How It Works (3 easy steps)

1

See what changed from Trip A to Trip B. Did we add apples? bananas? both?

2

Find the money change: Δ = T₂ − T₁.

3

If only one fruit changed, the price of that fruit is Δ ÷ (how many more). If both changed, make a small replacement to match one fruit, then use Step 3.

Tip: Work in simple numbers (rupiah) and keep the same unit everywhere.

Example 1 (Only bananas change)

Trip A: 2 apples + 3 bananas = Rp 8,600

Trip B: 2 apples + 5 bananas = Rp 10,000

Only bananas changed: +2 bananas
Money change: Δ = 10,000 − 8,600 = 1,400
One banana costs 1,400 ÷ 2 = Rp 700
Back to Trip A: 2 apples + 3×700 = 8,600 ⇒ 2 apples = 6,500 ⇒ one apple = Rp 3,250

Example 2 (Both change → small replacement)

Trip A: 3 apples + 2 bananas = Rp 9,700

Trip B: 5 apples + 1 banana = Rp 12,100

Make bananas match: replace 1 apple in Trip B with 1 banana → (4 apples + 2 bananas).
This “swap” changes money by exactly the price of one apple − one banana.
Now compare (3a+2b) → (4a+2b): the change is one apple.
Money change: 12,100 − (price after swap). We can calculate this neatly with the tool below!

Try It Yourself

🧺 Fill in two trips. Use small numbers. Press Solve.

Trip A apples Trip A bananas Rp T₁

Trip B apples Trip B bananas Rp T₂

Answer will appear here.

Practice — Easy

Trip A: 1 apple + 4 bananas = Rp 6,500
Trip B: 1 apple + 6 bananas = Rp 8,100
Show answer
Bananas change by +2. Δ=1,600 ⇒ banana=Rp 800. Then apple=6,500−4×800=3,300.
Trip A: 3 apples + 1 banana = Rp 10,000
Trip B: 3 apples + 4 bananas = Rp 12,400
Show answer
Bananas +3. Δ=2,400 ⇒ banana=Rp 800. Then apple=(10,000−800)/3=3,067.

Practice — Both Change

Trip A: 2 apples + 2 bananas = Rp 9,000
Trip B: 5 apples + 1 banana = Rp 14,500
Show steps
Make bananas match: change Trip B to 4 apples + 2 bananas by replacing 1 apple with 1 banana.
Compare 2a+2b → 4a+2b: +2 apples causes money change = 14,500 − (price after swap). Use the tool to compute exactly.

Teacher Notes

Keep whole numbers where possible. Use local currency.
First teach the “only one thing changed” cases. Then show one gentle replacement.
Let students explain in words before writing any symbols.