Nancy and Sally were sisters born five years apart. Despite their age difference, the sisters were very close.

The years passed and both sisters grew up, married, and settled down and had children. The families lived just up the street from each other, and the kids played together every day. Life was good.

Between the two couples, they had 6 children. Nancy’s son, Jeremy, was the oldest of them all at age 15.

He was a smart, well-rounded kid, and was a good role-model for all the other children.

One day, Sally took Jeremy and 3 of the other children out to lunch at their favorite pizza place.

Between the 5 of them, they ordered 4 slices of cheese pizza, and 3 slices of pepperoni pizza.

Cheese pizza cost $2 per slice, pepperoni cost $3. She had a coupon for $1 off a slice of pizza.

She handed the coupon to the pimply teenager behind the register.

“Ok, that’ll come out to $16” said the cashier.

Sally thought for a second. Then she smiled.

“No, shouldn’t it be $32? I think you did your math wrong?”

The cashier paused.

“No ma’am, $16 is correct”

“No, no, no,” said Sally, “I’m afraid you are mistaken, and I don’t want you to undercharge me. Here, I’ll show you.”

She took out a pen and scribbled on the back of an old receipt.

“Look, so I got 4 slices of cheese and 3 slices of pepperoni. The cheese was a two dollars and pepperoni was three. And I had that coupon.”

She jotted down her math, and again arrived at $32. The cashier was dumbfounded. How could he have been so far off?

Jeremy glanced down at her paper and realized immediately what was going on.

He stepped in to clear up the confusion.

“Uh, sir,” he said to the cashier, “Please Excuse My Dear Aunt Sally.”

He continued, “She didn’t follow the order of operations. She’s added and subtracted before she’s multiplied. She made this same mistake last week when she completely ignored some parenthesis.”

Sally turned bright red.

Jeremy continued, “So, Aunt Sally, the $16 is correct. And that booth in the corner just opened up, so I’m going to grab it for us. Can you get me a Sprite? And make sure to leave a 20% tip.”

Jeremy walked off with one of his cousins and sat at the table.

Sally turned back to the cashier and scratched her head. She laughed nervously as she flipped through her purse.

“Uhhh… This should cover it,” she said, and she handed the cashier a $100 bill.