14 CHAPTER 1 Critical Thinking Skills e) The most electricity was used in July 2024. Approximately 2400 kWh of electricity were used. f) In January 2024, about 1200 kWh were used. Write 10.0127 cents as $0.100127. Rounding the rate to $0.10 per kWh and multiplying by 1200 yields an estimate of $120. 0.10 1200 $120 × = Thus, the cost of electricity in January 2024 was about $120. 7 Now try Exercise 41 Example 7 Estimating the Number of Corn Kernels in a Photo Estimate the number of corn kernels in the top layer in the accompanying photograph. Solution To estimate the number of kernels, we can divide the photograph into rectangles with equal areas and then select one area that appears to be representative of all the areas. Estimate (or count) the number of kernels in this single area and then multiply this number by the number of equal areas. Let’s divide the photo into 20 approximately equal areas. We will select the left region in the top row as the representative region. We enlarge this region and count the kernels in it. If half a kernel is in the region, we count it (see the following enlargement). There are about 18 kernels in this region. Multiplying by 20 gives 18 20 360. × = Thus, there are about 360 kernels in the photo. 7 Now try Exercise 47
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