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Video: Understanding Subtraction in Word Problems Involving Decimal Numbers

Kathryn Kingham

Natalie has $45 to buy chocolate. A white chocolate bar costs $3.87, and a dark chocolate bar costs $3.59. If Natalie buys 7 bars of white chocolate for $27.09, how can she determine the amount of money she has left to buy dark chocolate? [A] Subtract $3.59 from $3.87 [B] Add $3.87 and $3.59 [C] Subtract $27.09 from $45 [D] Add $3.59 and $27.09 [E] Subtract $3.59 from $45

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Video Transcript

Natalie has 45 dollars to buy chocolate. A white chocolate bar cost three dollars and 87 cents. And a dark chocolate bar cost three dollars and 59 cents. If Natalie buys seven bars of white chocolate for 27 dollars and nine cents, how can she determine the amount of money she has left to buy dark chocolate?

Natalie has 45 dollars to buy chocolate. She is interested in buying white chocolate and dark chocolate. Her 45 dollars will have to equal the white chocolate cost plus the dark chocolate cost. We know that Natalie spent 27 dollars and nine cents on the white chocolate. 27 dollars and nine cents plus the amount of dark chocolate has to equal 45 dollars.

How can we find out what that dark chocolate cost would be? We would have to take the money that Natalie started with, subtract what was already spent, the white chocolate. And that would leave us with the remaining money. Let’s fill in the blanks here.

Natalie’s starting money was 45 dollars. Subtract the money she already spent, the cost of the white chocolate, 27 dollars and nine cents. This would be our model for solving the problem. Which of the answer choices gives us this? Subtract 27 dollars and nine cents from 45. There’s only one option that gives these instructions, option c), subtract 27 dollars and nine cents from 45 dollars.