Question 201879
1.  let t="30 sec commercials" and s="60 sec commercials"


"A disc jockey must play 16 commercial sports during 1 hour" ___ t + s = 16 ___ t = 16 - s


"total commercial time during 1 hour is 13 min" ___ 60t + 30s = 13 * 60


substituting ___ 60 (16 - s) + 30s = 13 * 60


960 - 60s + 30s = 780 ___ -30s = -180 ___ s = 6


substituting ___ t + 6 = 16 ___ t = 10



follow this same technique for the other questions




2. let s="scientific calcs" and g="graphing calcs"


"an order of 50 calculators" ___ s + g = 50 ___ s = 50 - g


"The Everton College store paid $1834"
" The store paid $ 10 each scientific calculator. The others, all graphing calculators, cost the store $56 each" ___ 10s + 56g = 1834


substituting ___ 10 (50 - g) + 56g = 1834
solve for g, and then substitute to find s



3. let L="lumber units" and p="plywood units"


"three times as many units of plywood as lumber" ___ p = 3L


"it makes a profit of $30 on a unit of lumber and $45 on a unit of plywood. How many of each unit must produced and sold in the order to make a profit of $16830"
30L + 45p = 16830


substituting ___ 30L + 45 (3L) = 16830
solve for L, and substitute to find p