Question

Which set of steps could be used to solve this story problem? Helen read 4 books per week for the first 3 weeks of her summer vacation. She read 2 books per week for the last 4 weeks. She also read 2 magazines each week. How many books did Helen read over summer vacation? A. Multiply 4 by 3. Then multiply 2 by 4. Add the two products. B. Add 3 and 4. Then add 2 and 4. Add the two sums. C. Multiply 3 × 4. Then add 4 to that product. Then subtract 2. D. Add 4 and 4. Then divide that sum by 2 and add 3 to the quotient.

Answer 1

A. Multiply 4 by 3. Then multiply 2 by 4. Add the two products.

Explanation:

As with many rate problems, ...

quantity = rate · time

The total quantity will be the sum of quantities associated with different rates or time periods:

total quantity = quantity1 + quantity2

= (rate 1)(time 1) + (rate 2)(time 2)

= (4 books/week)(3 weeks) + (2 books/week)(4 weeks)

= 4·3 books + 2·4 books . . . . . . units of (weeks/weeks) cancel

= (4·3 + 2·4) books . . . . . . formula matches selection A