21. The number who responded is 600 -150 = 450. Expressed as a fraction of the total, that is
450/600 = (150*3)/(150*4) = 3/4
22. Total fabric used is
6*(3 1/6) +8*(2 3/4) = 19 +22 = 41 . . . . yards
Fabric unused is . . .
50 yd -41 yd = 9 yd
23. The problem statement is ambiguous. We suppose it is intended to say that the stock increased by 1/4 of its original value. In that case, the present value is
$2000 +$2000*(1/4) = $2500
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An alternate interpretation of the statement is that the amount of increase was 1/4. In that case, the present value is
$2000 + 0.25 = $2000.25