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62 Rh 23. A man has a dollars and b dimes, how many cents has he ? 24. If I spend x half-dollars out of a sum of $20, how many half-dollars have I left ? 25. Out of a purse containing $a and b dimes a man spends c cents ; express in cents the sum left. 26. By how much does 2 x — 5 exceed x+ 1? 27. What number must be taken from a— 2b to leave a— 3 b? 28. If a bill is shared equally amongst x persons, and each pays four dimes, how many cents does the bill amount to ? 29. If I give away c dimes out of a purse containing a dollars and b half-dollars, how many dimes have I left ? 30. If I spend x quarters a week, how many dollars do I save out of a yearly income of $y ? 31. A bookshelf contains x Latin, y Greek, and z English books ; if there are 100 books, how many are there in other languages ? 32. I have x dollars in my purse, y dimes in one pocket, and z cents in another ; if I give away a half-dollar, how many cents have I left? 33. In a class of x boys, y work at Classics, z at Mathematics, and the rest are idle; what is the excess of workers over idlers ?

84. We add a few harder examples worked out in full.

Ex. 1. What is the present age of a man who x years hence will be m times as old as his son now aged y years ?

In x years the son's age will be y + x years ; hence the father's age will be m(y + x) years ; therefore now the father's age is m(y + x) — x years.

Ex. 2. Find the simple interest on $ k in n years at f per cent. Interest on $100 for 1 year is $f, $1 ${f}{100}, $k ${kf}{100}, Interest on k for n years is ${nkf}{100}.

Ex. 3. A room is x yards long, y feet broad, and a feet high ; find how many square yards of carpet will be required for the floor, and how many square yards of paper for the walls.