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The cumulative costs of a tankless water heater and tank water heater are 
$4,090 each at the end of the 
7^("th ") year of use. The cumulative costs of the tankless heater increase 
$180 per year, but for the tank heater, they increase by 
11% per year. By the end of the 
10^("th ") year, about how much more will the cumulative costs of the tank heater be than those of the tankless heater?
Choose 1 answer:
(A) 
$964
(B) 
$1,504
(C) 
$4,625
(D) 
$5,723

The cumulative costs of a tankless water heater and tank water heater are $4,090\$4,090 each at the end of the 7th7^{\text{th}} year of use. The cumulative costs of the tankless heater increase $180\$180 per year, but for the tank heater, they increase by 11%11\% per year. By the end of the 10th10^{\text{th}} year, about how much more will the cumulative costs of the tank heater be than those of the tankless heater?\newlineChoose 11 answer:\newline(A) $964\$964\newline(B) $1,504\$1,504\newline(C) $4,625\$4,625\newline(D) $5,723\$5,723

Full solution

Q. The cumulative costs of a tankless water heater and tank water heater are $4,090\$4,090 each at the end of the 7th7^{\text{th}} year of use. The cumulative costs of the tankless heater increase $180\$180 per year, but for the tank heater, they increase by 11%11\% per year. By the end of the 10th10^{\text{th}} year, about how much more will the cumulative costs of the tank heater be than those of the tankless heater?\newlineChoose 11 answer:\newline(A) $964\$964\newline(B) $1,504\$1,504\newline(C) $4,625\$4,625\newline(D) $5,723\$5,723
  1. Calculate Tankless Water Heater Cost: Determine the cumulative cost of the tankless water heater after 1010 years.\newlineWe know that the cumulative cost of the tankless water heater is $4,090\$4,090 at the end of the 77th year. It increases by $180\$180 per year. Therefore, for the next 33 years (88th, 99th, and 1010th year), we need to add this annual increase to the initial cost.\newlineCumulative cost after 1010 years = Initial cost + (Annual increase ×\times Number of years)\newline= $4,090+($180×3)\$4,090 + (\$180 \times 3)\newline= $4,090+$540\$4,090 + \$540\newline= $4,630\$4,630
  2. Calculate Tank Water Heater Cost: Determine the cumulative cost of the tank water heater after 1010 years.\newlineThe cumulative cost of the tank water heater is also $4,090\$4,090 at the end of the 77th year. It increases by 1111% per year. We need to calculate the compound increase for the next 33 years.\newlineFor the 88th year: $4,090×(1+11100)=$4,090×1.11\$4,090 \times (1 + \frac{11}{100}) = \$4,090 \times 1.11\newlineFor the 99th year: ($4,090×1.11)×1.11(\$4,090 \times 1.11) \times 1.11\newlineFor the 1010th year: (($4,090×1.11)×1.11)×1.11((\$4,090 \times 1.11) \times 1.11) \times 1.11\newlineCumulative cost after 1010 years = $4,090×(1.11)3\$4,090 \times (1.11)^3
  3. Calculate Tank Water Heater Compound Increase: Calculate the cumulative cost of the tank water heater after 1010 years.\newlineCumulative cost after 1010 years = $4,090×(1.11)3\$4,090 \times (1.11)^3\newline= $4,090×1.11×1.11×1.11\$4,090 \times 1.11 \times 1.11 \times 1.11\newline= $4,090×1.367631\$4,090 \times 1.367631\newline$5,594.77\approx \$5,594.77
  4. Calculate Difference in Cumulative Costs: Calculate the difference in cumulative costs between the tank water heater and the tankless water heater after 1010 years.\newlineDifference = Cumulative cost of tank heater - Cumulative cost of tankless heater\newline= $5,594.77$4,630\$5,594.77 - \$4,630\newline$964.77\approx \$964.77

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