Question

Estimate each problem to check if the student's answer is reasonable. If not, cross

out the answer and write the correct answer. Show your work.
Problems
1 1.3-(-2.5)
Student Answers
-1.2
3.8
Possible estimate: 1-(-3)=1+3
= 4
1.3-(-2.5) = 1.3 +2.5
= 3.8

Answer 1

The student's estimate of 3.8 for the subtraction problem 1.3 - (-2.5) is reasonable, matching the properly calculated exact answer when following the addition rules for numbers with opposite signs.

Step-by-step explanation:

When evaluating whether the student's answer is reasonable, we must first look at the problem presented, which is 1.3 - (-2.5). The student suggests two possible answers: -1.2 and 3.8. To estimate, we can round 1.3 down to 1 and -2.5 up to -3 to make it simpler.

According to the rules of subtraction, we change the sign of the number being subtracted and then follow the rules of addition, which would give us 1 - (-3) = 1 + 3 = 4.

Comparing this estimate of 4 with the student's answers, we can see that 3.8 is a reasonable approximation of 4 and is thus the correct answer, while -1.2 is not reasonable. To prove this, we add 1.3 and 2.5 directly to get the exact answer, which indeed is 3.8, matching the student's second solution.