Question

Erin and Jamie are collecting shells while the tide is out. Erin has 27 shells, and she has 9 more than Jamie. Write and equation for this situation and find how many shells Jamie has collected.

A. 27 = j + 9; Jamie collected 18 shells
B. 27 = j – 9; Jamie collected 36 shells
C. 27 + 9 = j; Jamie collected 36 shells
D. 27 = j + 9; Jamie collected 36 shells

Answer 1

A.

Erin's total minus 9 gives us Jamie's total. This means Erin's total equals Jamie's total plus 9. This leads us to the conclusion that 27 (E's total) = j + 9 (the difference). We also know from the first phrase that E - 9 = j, meaning 27 - 9 = j, so j = 18.

Answer 2

The correct answer is A.

Explanation:

The main idea in this kind of exercises is to ‘‘translate’’ from natural language to mathematical language.

We know that Erin has 27 shells. If we use the variable E for the number of shells that Erin has, we ‘‘translate’’ the previous fact as E=27.

The next data is that Erin has 9 shells more than Jamie. Let us write J for the number of shells that Jamie has. The fact that Erin has 9 shells more than her partner means that Jamie would need 9 shells more to has the same amount of shells. Mathematically this means that J+9=E.

Then, substituting the value of E we get J+9=27. The last step is to obtain the value of J: J=27-9.