4. To keep cool in the summer months, you decide to design and build your own hand-held fan. The fan's electrical circuit will run off of 4 AA batteries (each with a voltage of 1.5 V) and must not exceed 50 mA of
current. You visit your local Radio Shack and find that resistors are sold in five varieties: 5 Ohm, 10 Ohm, 12
Ohm, 20 Ohm, 50 Ohm. Each resistor costs 8 cents. What set of resistors should you buy to minimize cost?

Atank holds 1000 gallons of water, which drains from the bottom of the tank in half an hour. the values in the table show the volume v of water remaining in the tank (in gallons) after t minutes.t(min) 5 10 15 20 25 30v(gal) 694 444 250 111 28 0(a) if p is the point (15, 250) on the graph of v, find the slopes of the secant lines pq when q is the point on the graph with t = 5, 10, 20, 25, and 30.(b) estimate the slope of the tangent line at p by averaging the slopes of two secant lines.(c) use a graph of the function to estimate the slope of the tangent line at p. (this slope represents the rate at which the water is flowing from the tank after 15 minutes.)show all steps.

If gases like carbon dioxide and methane make up less than 1% of the total atmosphere, why is it important for scientists to monitor changes in percentages of these gases?

How is sound energy produced a. vibrating objects b. objects being heated c. temperature differences d. stationary objects