1. A thin convex-concave lens has rays from the convex surface 25.0 cm and from the concave surface 61.0 cm. If the glass used has a refractive index of 1.5, what is its focal length? Give the answer in cm.

2. A pipe with an open end and a closed end produces a fundamental frequency of 330 Hz. How long is it (what is the pipe's length)? (the speed of sound in air is 340 m/s)