Question

Which of the following options uses the ‘make a $10$’ strategy. Find out the correct difference between $14$ and $7.$

• A.
• B.
• C.
• D.

Answer 1

The correct option is C

Say: Let’s read the question and observe the given solutions in the option.

Ask:
$\bullet$ How can we subtract using the make a ten strategy?
Ans: To use the make a ten strategy to subtract, we have to first break down the smaller number such that one of the decomposed numbers when subtracted from the bigger number will make $10$. Then, we subtract the other remaining decomposed number from $10$ to find the answer.
$\bullet$ What is the first step to finding the difference between $14$ and $7$ using the make a ten strategy, and why?
Ans: We need to decompose $7$ into $4$ and $3$ because $4$, when subtracted from $14$, makes $10$.
$\bullet$ What do we do next?
Ans: We subtract $3,$ the other decomposed number, from $10$ to find the answer.
$\bullet$ What is the answer?
Ans: $7$
$\bullet$ Is option A the correct solution, and why?
Ans: No because in this solution, $7$ is split into $4$ and $3$, then $4$ is subtracted from $14$ to make $10$ but then again instead of $3,4$ is subtracted from $10.$
$\bullet$ Is option B the correct solution, and why?
Ans: No because in this solution, $7$ is split into $5$ and $2$. 5 subtracted from $14$ makes $9$ and not $10.$ So in the option $10$ is incorrect, thus the option is also incorrect.
$\bullet$ Is option C the correct solution, and why?
Ans: Yes because in this solution, $7$ is split into $4$ and $3$, then $4$ is subtracted from $14$ to make $10.$ Then further, $3$ is subtracted from $10$ to get $7$ as the answer.
$\bullet$ Is option D the correct solution, and why?
Ans: No because in this solution, $7$ is split into $5$ and $2.5$ subtracted from $14$ makes $9$ and not $10.$ So in the option also $10$ is incorrect, thus the option is also incorrect.

Hence, option C is the correct answer.

WB: Use the whiteboard to show the correct solution.

Probing Question:
Q. While subtracting $7$ from $14$, after splitting $7$ into $5$ and $2,$ if we subtract $2$ from $14$ to make $12,$ then subtract $5$ from $12$ to get $7$ as the answer, will this also be called a “make a ten” strategy?
A: No, because though we will get the correct answer, we are not making a ten here to subtract. So, this will not be a “make a ten” strategy to subtract.