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MediumFreeREDUCELAMBDA

REDUCE: price after stacked discounts

During a double-date sale, Wira's electronics store stacks three discounts on a laptop: a 20% store discount, then a 10% voucher, then a 5% member cashback. Many buyers assume that adds up to 35%, but each discount applies to the price left after the previous one.

Task

Fill in two cells:

B8: one REDUCE + LAMBDA formula that starts from the regular price in B1, then applies each discount in B4:B6 in turn (price × (1 − discount)).
B9: the real total discount percentage, 1 − B8/B1 (a regular formula).

Cells to fillB8B9

Required functionsREDUCELAMBDA

Expected result

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Hint 1
REDUCE(initial_value, array, LAMBDA(accumulator, value, …)) walks through the array one item at a time and carries the running result (the accumulator) to the next step. The final result is a single value.
Hint 2
The initial value is the regular price in B1. At each step, the accumulator is the current price and the value is one discount.
Hint 3
Pattern: =REDUCE(B1, B4:B6, LAMBDA(price, d, …)). The last part: price times (1-d).

Reveal them one at a time. The last hint nearly gives the answer away.

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Answer

B8

=REDUCE(B1,B4:B6,LAMBDA(price,d,price*(1-d)))

B9

=1-B8/B1

Explanation

=REDUCE(B1,B4:B6,LAMBDA(price,d,price*(1-d))) runs three steps: 12,000,000 × 80% = 9,600,000, then × 90% = 8,640,000, then × 95% = 8,208,000. The total discount is only 31.6%, not 35%. The difference from SCAN: REDUCE returns only the final result, while SCAN returns every step. =B1*PRODUCT(1-B4:B6) gives the same answer, but REDUCE handles trickier rules, such as a discount with a maximum cap.

Starting worksheet: Sheet1
Row	A	B
1	Regular price	12,000,000
2
3	Discount step	Rate
4	Store discount	20%
5	Voucher	10%
6	Member cashback	5%
7
8	Final price
9	Real total discount
10
11
12
13
14

Fill in the requested cells, then press Check answer.

Validation result