Lucita does the division problem 3.302 ÷ -1.27, and gets -0.026. She doesn't understand this result because she had estimated the answer to be -3. What was Lucita's mistake?

The decimal point should be to the left of the 6.
Lucita's estimate is too low.
Lucita's estimate is too high.
The decimal point should be to the left of the 2.

1 answer

To understand Lucita's mistake, let's first analyze the division problem \(3.302 \div -1.27\).

  1. If we ignore the negative sign and simply consider \(3.302 \div 1.27\):

    • To get an estimate, we can round \(3.302\) to \(3.3\) and \(1.27\) to \(1.3\).
    • Then we can estimate \(3.3 \div 1.3\).
  2. To make this division easier, we can convert these numbers into fractions:

    • \(3.3 \div 1.3\) is similar to \(\frac{33}{10} \div \frac{13}{10} = \frac{33}{13}\).
    • A rough estimate for \(\frac{33}{13}\) is approximately \(2.54\) (because \(13\) goes into \(33\) about \(2.5\) times).
  3. Now accounting for the sign, since we are dividing a positive number by a negative number, the result would be negative. Thus, our estimated result should be around \(-2.54\).

  4. Lucita, however, estimated the result to be \(-3\). This estimate of \(-3\) is too low compared to the actual result.

Considering her actual result of \(-0.026\), which is much smaller in magnitude than her estimate of \(-3\), it suggests that she misunderstood the scale of the numbers involved in the division.

So, the correct assessment of her mistake is that Lucita's estimate is too low.