AMC 10 · 2016 · #2

Grade 6 arithmetic
exponentsfunction-evaluationfraction-arithmetic formula-substitution ↑ Prerequisites: exponents
📏 Medium solution 💡 1 insight
Problem
A made-up operation is defined by n♥ m = n³ m². Using this rule, find the value of the fraction (2♥ 4)/(4♥ 2).

Pick an answer.

(A)
$\frac{1}{4}$
(B)
$\frac{1}{2}$
(C)
1
(D)
2
(E)
4

AMC 10 2016 problem © Mathematical Association of America (MAA AMC). Reproduced for educational use.

How to solve
Strategy Introduce a Variable

The heart symbol is a brand-new operation, so the whole problem is really about reading its rule n♥ m = n³ m² correctly and substituting the right number into the right slot. Tool #4 (Introduce a Variable) is exactly that: treat n and m as labeled slots, plug in the given numbers, and respect that the first slot is cubed while the second is squared. Tool #7 (Identify Subproblems) splits the work into two clean calculations — the top 2♥ 4 and the bottom 4♥ 2 — so they never get tangled. Tool #3 (Eliminate Possibilities) then matches the reduced fraction to the one correct choice.

1STEP 1

Read the rule's two slots

The rule n♥ m = n³ m² cubes the first slot, squares the second, so order matters and 2♥ 4 ≠ 4♥ 2.

n♥ m = n³ m² (first input cubed, second input squared)
2STEP 2

Compute the numerator

Top 2♥ 4: cube the first, square the second — 2³ = 8 and 4² = 16, so the numerator is 128.

2♥ 4 = 2³ · 4² = 8 · 16 = 128
3STEP 3

Compute the denominator

Bottom 4♥ 2 swaps the slots: 4³ = 64 and 2² = 4, so the denominator is 256 — larger than the top.

4♥ 2 = 4³ · 2² = 64 · 4 = 256
4STEP 4

Divide and simplify

The fraction is 128/256, and since 256 = 2 × 128 it reduces to 1/2 — matching choice (B).

128/256 = 128/(2 · 128) = 1/2 = (B)
Answer
1/2
The denominator 4♥ 2 gives the larger number 4 the cube, while the numerator 2♥ 4 gives the larger number only a square, so the top should be smaller than the bottom and the fraction should be less than 1. The result 1/2 fits that expectation, and it matches choice (B).
💡Key takeaway

When a problem invents a new symbol, treat it as a recipe with labeled blanks — fill in the right number, and remember the order can change the answer.

  • Read the rule's two slots
  • Compute the numerator
  • Compute the denominator
  • Divide and simplify