A diner has 645 napkins. 325 napkins are used at lunch. 113 napkins are used at dinner.
Melanie says that
325
−
113
=
n
napkins are used in all, and that
645
−
212
=
r
napkins are left.
Is her answer reasonable? Explain why or why not.
Part A
Is her answer reasonable?
A.
No, because at least 325 napkins are used. So, 212 is too small a number for n.
B.
No, because she adds the number of total napkins used to find n.
C.
No, because she makes an error in her subtraction.
D.
Yes, her answer is reasonable.
Part B
Choose the equations you could use to find the number of napkins that remain after lunch and dinner.
t
represents the napkins that remain after lunch and dinner.
A.
325
−
113
=
t
B.
645
−
438
=
t
C.
645
−
325
=
t
D.
645
−
212
=
t
12 / 16
11 of 16 Answered
Part A:
The correct answer is A. No, because at least 325 napkins are used. So, 212 is too small a number for n. Melanie's answer is not reasonable because it implies that the total number of napkins used for lunch and dinner is only 212, which is less than the number of napkins used at lunch alone.
Part B:
The equations we could use to find the number of napkins that remain after lunch and dinner are C. 645 - 325 = t, or D. 645 - 212 = t.
Option A (325 - 113 = t) finds the total number of napkins used at lunch and dinner, not the number of napkins that remain. Option B (645 - 438 = t) finds the number of napkins used at lunch and dinner but subtracts the wrong amount. this is correct?
Yes, that is correct. Option A finds the total number of napkins used, not the number of napkins that remain. Option B subtracts the wrong amount, as it subtracts the total number of napkins used instead of just the number used at lunch and dinner.
Part A: Yes, this is correct. Melanie's answer is not reasonable because it implies that the total number of napkins used for lunch and dinner is only 212, which is less than the number of napkins used at lunch alone.
Part B: Yes, this is correct. Option C (645 - 325 = t) finds the number of napkins that remain after lunch and dinner. Option D (645 - 212 = t) also finds the number of napkins that remain after lunch and dinner.