The Lisa Frank store in Fayette Mall had total sales of $1,800,000. The stationery department sales were 15% of the store’s total sales. The apparel department sales were 45% of total sales. What were the dollar sales for the stationery department? Solution The dollar sales for the stationery department were: = $1,800,000 × 15% = $270,000.

1. The photoreceptors in the human eye, called rods and cones, have different sensitivities to
different wavelengths of electromagnetic waves. (Figure 1) (Notice that the y axis in the figure is
a logarithmic scale.) The rods, which number over 100 million, can only be activated by a certain
range of wavelengths, but they do not pass any color information to the brain. In other words,
they note differences in shades of grey (from black to white) and are responsible for a person's
ability to see in dim light. Cones, which number around 6 million, give us color vision. Cones
come in three different kinds: 64% of cones are sensitive to long wavelengths of visible light
(toward the red end of the spectrum), 32% are sensitive to medium wavelengths, and the
remaining 2% are sensitive to short wavelengths (toward the blue end of the spectrum). Colors
are differentiated on the basis of the extent to which visible light stimulates each kind of cone.
a) Do rods have their peak sensitivity at a higher or lower frequency than cones?
b) Do rods and cones have similar sensitivities near the red or near the violet edge of the visible
spectrum?
c) Is it easier to detect a dim red source or a dim violet source of light?
Solution
a)Rods have peak sensitivity at higher frequency than cones...... this can be understood if we
analyze logaritmic relative sensitivity graph vs wavelength
b) they have similar sensitivity at higher wavelength which means lower frequency
so the answer is near the red region
c) It is easier to detect a dim violet source