AMC 8 · 2020 · #2

Easy mode Grade 3

Problem

Imagine four friends who spent the weekend doing yardwork. One friend earned $\$15$ . Another earned $\$20$ . A third earned $\$25$ . The last friend earned $\$40$ .

They decide to put all their money together and then split it equally, so each friend ends up with the same amount.

The friend who earned $\$40$ has more than a fair share. How much does that friend need to give to the others?

Pick an answer.

(A)

$\$5$

(B)

$\$10$

(C)

$\$15$

(D)

$\$20$

(E)

$\$25$

AMC 8 2020 problem © Mathematical Association of America (MAA AMC). Reproduced for educational use.

Try it yourself first — the explanation is most useful after you’ve attempted it.

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Toolkit + CCSS Solution

Understand

Restated: Four friends did yardwork and earned $\$15$, $\$20$, $\$25$, and $\$40$. They want to pool everything and end up with equal amounts. How much money does the friend who earned $\$40$ hand over to the rest of the group?

Givens: Earnings of the four friends: $\$15$, $\$20$, $\$25$, $\$40$; The four friends split their combined earnings equally (so each ends up with the same amount); Answer choices: (A) $\$5$, (B) $\$10$, (C) $\$15$, (D) $\$20$, (E) $\$25$

Unknowns: The total dollar amount the $\$40$-earner gives away to the other three friends

Understand

Plan

Primary tool: #7 Identify Subproblems

Secondary: #3 Eliminate Possibilities

The question hides three smaller, easier questions inside it: (1) what is the total pile of money? (2) what is each friend's fair share? (3) how much more than the fair share did the $\$40$ friend start with? Tool #7 (Identify Subproblems) is perfect because solving these three pieces in order turns a one-line word problem into three single-step arithmetic problems we can already do. Tool #3 (Eliminate Possibilities) is held in reserve: once we have an answer, we can confirm it against the five multiple-choice options to make sure no arithmetic slip occurred.

Execute — Answer: C

#7 Identify Subproblems 3.NBT.A.2 Step 1

Add the four amounts

Subproblem 1 — find the total earnings.
Add the four amounts together to see how much money the group has to share.

$\$15 + \$20 + \$25 + \$40 = \$100$

💡 Adding four whole-dollar amounts that are all under $\$50$ is a Grade 3 "add within $1000$" calculation.

#7 Identify Subproblems 3.OA.A.3 Step 2

Divide into equal shares

Subproblem 2 — find each friend's fair share.
"Split equally among four" means divide the total by $4$, the same operation as sharing $100$ cookies among $4$ kids.

$\$100 \div 4 = \$25 \text{ per friend}$

💡 "Share equally among four" is the Grade 3 fair-share division word-problem move.

#7 Identify Subproblems 3.NBT.A.2 Step 3

Find the extra to give away

Subproblem 3 — find how much the $\$40$ friend must give up. He starts with $\$40$ but should end with $\$25$, so the gap is what he hands to the others.

$\$40 - \$25 = \$15 \;\Rightarrow\; \textbf{(C)}$

💡 Subtracting $25$ from $40$ is a Grade 3 single-step subtraction within $100$.

#3 Eliminate Possibilities 3.NBT.A.2 Step 4

Verify the result

Verify with Tool #3 (Eliminate Possibilities).
Check the answer against the five choices: only $\$15$ matches the gap between $\$40$ and the $\$25$ fair share. (A) $\$5$ would leave him with $\$35$, (B) $\$10$ with $\$30$, (D) $\$20$ with $\$20$, (E) $\$25$ with $\$15$ — none of those equals $\$25$.

$\$40 - \$15 = \$25 \checkmark$

💡 Plugging each choice back and subtracting from $\$40$ is still Grade 3 subtraction — perfect for a quick double-check.

[1] #7 3.NBT.A.2 Subproblem 1 — find the total earnings. Add the four amounts together to see how

[2] #7 3.OA.A.3 Subproblem 2 — find each friend's fair share. "Split equally among four" means d

[3] #7 3.NBT.A.2 Subproblem 3 — find how much the $\$40$ friend must give up. He starts with $\$4

[4] #3 3.NBT.A.2 Verify with Tool #3 (Eliminate Possibilities). Check the answer against the five

Review

Reasonableness: Quick sanity check: the four amounts $\$15, \$20, \$25, \$40$ are not too different, so the fair share $\$25$ should sit roughly in the middle — which it does. The two friends below $\$25$ ($\$15$ and $\$20$) together need $\$10 + \$5 = \$15$ to reach $\$25$, and the friend at exactly $\$25$ needs nothing. So the $\$40$ friend must supply exactly $\$15$ — matching our answer (C). The books balance, which is exactly what "split equally" requires.

Alternative: Tool #6 (Guess and Check) on each answer choice. If the $\$40$ friend gives $\$15$ (choice C), he keeps $\$25$; the $\$15$ friend receives part of that and the $\$20$ friend receives the rest so everyone lands on $\$25$. None of the other choices let all four totals come out equal — for example giving $\$10$ leaves the $\$40$ friend with $\$30$, which is already above the fair share before anyone else gets paid. So (C) is the only consistent choice.

CCSS standards used (min grade 3)

3.NBT.A.2 Fluently add and subtract within 1000 (Adding the four earnings to get $\$100$, subtracting $\$25$ from $\$40$ to get the $\$15$ handed over, and checking answer choices with quick subtractions from $\$40$.)
3.OA.A.3 Solve multiplication and division word problems within 100 (Dividing $\$100$ equally among $4$ friends to get the $\$25$ fair share — a classic Grade 3 "share equally" division word problem.)

⭐ This AMC 8 problem only needs Grade 3 add-subtract and "share equally" division that you already know!

Toolkit + CCSS Solution

Understand

Plan

Execute — Answer: C

Add the four amounts

Divide into equal shares

Find the extra to give away

Verify the result

Review

CCSS standards used (min grade 3)

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