STANDARDS

CCSS: 4.NF.C.7, 5.NBT.B.7, MP2, MP3, MP8

TEKS: 4.4A, 4.8C, 5.3E

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The Case of the Lunchroom Losses

Caleb Craft is a young detective with a passion for math and a thirst for mystery. Can you match wits with him? Read this story carefully, thinking about the math clues. 

September 2020
By Jessica McKenna-Ratjen

Illustrations by David SanAngelo

“Oh no, not again!”

“What’s the problem, Mrs. Clabber?” Caleb asked. 

“The register is 55 cents short!” Mrs. Clabber exclaimed, shaking her head. 

“Can I take a look?” Caleb said. He noticed that the shiny register had the words AUTOCHANGE 2020 marked on the side. 

“This register is new. It dispenses change automatically,” said Mrs. Clabber. “I always have the right amount of change in the drawer at the start of  lunch. But by the end, exactly 55 cents are missing!”

“Don’t worry, Mrs. Clabber,” assured Caleb. “I’m on the case!”

The next day, Caleb dashed to lunch. He stood next to the fruit shelf, peering at the register.

Caleb watched the students pay for their lunches. Their change clinked automatically into the register tray. The prices of each item and the change given back added up correctly.

It was five minutes before the bell was about to ring, and everything seemed fine.

“What’s the problem, Mrs. Clabber?” Caleb asked.

“The register is 55 cents short!” Mrs. Clabber exclaimed. She shook her head.

“Can I take a look?” Caleb asked. The register was shiny. It had the words AUTOCHANGE 2020 marked on the side.

“This register is new. It gives change automatically,” said Mrs. Clabber. “I always have the right amount of change at the start of lunch. But 55 cents are missing by the end!”

“Don’t worry, Mrs. Clabber,” assured Caleb. “I’m on the case!”

Caleb dashed to lunch the next day. He stood next to the fruit shelf. He peered at the register.

Caleb watched the students pay for their lunches. Their change clinked automatically into the register tray. The prices of each item and the change back always added up correctly.

It was five minutes before the bell. Everything seemed fine.

Illustrations by David SanAngelo

Suddenly, 11 girls carrying field hockey sticks entered.

“That’s the field hockey team,” Mrs. Clabber chuckled. “They always come to lunch together. They get the same thing every day!”

Sure enough, each of the 11 girls picked out a single cup of $1.75 cheese fries. The team captain, Marcie, handed Mrs. Clabber two $1 bills to pay for her fries. But the register didn’t give the change Caleb expected. 

Caleb watched closely. The same thing happened when the other 10 girls paid. Two $1 bills went into the register, but it didn’t give back any quarters. 

Caleb questioned Mrs. Clabber about it.

“The machine always runs out of quarters just before they arrive,” Mrs. Clabber said. “But it’s programmed to use smaller-valued coins instead.”

“Hmm,” Caleb pondered. “I’ll be right back.”

Caleb found Marcie at the condiment station. “Hey, Marcie! Could I take a look at the change you just received?”

Suddenly, 11 girls carrying field hockey sticks entered.

“That’s the field hockey team,” Mrs. Clabber chuckled. “They always come to lunch right after practice. They get the same thing every day!”

Each of the 11 girls picked out a single cup of cheese fries. Each cup cost $1.75. Marcie was the team captain. She handed Mrs. Clabber two $1 bills. But the register didn’t give the change Caleb expected.

Caleb watched closely. The other 10 girls paid. The same thing happened each time. Two $1 bills went into the register. But the register didn’t give back any quarters.

Caleb asked Mrs. Clabber about it.

“The machine always runs out of quarters just before they arrive,” Mrs. Clabber said. “But it’s programmed to use coins with smaller values instead.”

“Hmm,” Caleb said. “I’ll be right back.”

Caleb found Marcie at the sauce station. “Hey, Marcie! Can I see the change you just got back?”

Illustrations by David SanAngelo

“Sure!” Marcie fished in her pocket and pulled out two dimes and two nickels.

“Did you have any coins before lunch?” Caleb asked.

Marcie shook her head. “Nope! Our team is doing a fund-raiser. All of our change goes  into the jar in Coach’s office.”

“Aha,” exclaimed Caleb.

Mrs. Clabber had the register  open when Caleb came back. “Another 55 cents gone,” she sighed.

“And I know why,” Caleb grinned.

“Why?” asked Mrs. Clabber. 

Caleb nodded at the AUTOCHANGE 2020. 

“Turns out your new register has been making donations to the field hockey fund-raiser! You’ll have to get it reprogrammed, and I can tell you why.”

“Sure!” Marcie fished in her pocket. She pulled out two dimes and two nickels.

“Did you have any coins before lunch?” Caleb asked.

Marcie shook her head. “Nope! Our team is doing a fund-raiser. All of our change goes into the jar in Coach’s office.”

“Aha,” Caleb exclaimed.

Caleb came back to the register. Mrs. Clabber had the register open. “Another 55 cents gone,” she sighed.

“And I know why,” Caleb grinned.

“Why?” asked Mrs. Clabber.

Caleb nodded at the AUTOCHANGE 2020.

“Your new register has been making donations to the field hockey fund-raiser! You’ll have to get it reprogrammed. I can tell you why.”

MATH TALK

How did Caleb crack the case? What really happened?  

MATH TALK

How did Caleb crack the case? What really happened?  

Decimal Operations

Hey, detectives! You’ll be one step closer to cracking the case if you try these math problems.

Decimal Operations

Hey, detectives! You’ll be one step closer to cracking the case if you try these math problems.

$1.50 + $0.50 =

$1.50 + $0.50 =

$3.25 – $0.85 = 

$3.25 – $0.85 = 

$0.10 × 6 = 

$0.10 × 6 = 

$1.00 ÷ 4 = 

$1.00 ÷ 4 = 

Continue the Learning Journey

  • Look through a grocery store circular or catalog and pick out two items, noting their prices. Write a combination of bills and coins that match the price of your items.
  • Pretend you manage a school cafeteria. Create a menu of food that you would serve over one school week. Then write a paragraph explaining your choices. Be sure to think about factors such as variety of foods, healthy choices, kids’ tastes, and so on.

Continue the Learning Journey

  • Look through a grocery store circular or catalog and pick out two items, noting their prices. Write a combination of bills and coins that match the price of your items.
  • Pretend you manage a school cafeteria. Create a menu of food that you would serve over one school week. Then write a paragraph explaining your choices. Be sure to think about factors such as variety of foods, healthy choices, kids’ tastes, and so on.
Financial Literacy
Money Subtraction, Money Addition, Money Division, Money Multiplication
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