1) 400 дм = 400:10 = 40 м.
20 а = 20*100 = 2000 кв.м.
A = S:B = 2000:40 = 50 м = 500 дм.
2) 30 мм = 3 см.
B = S:A = 78:3 = 26 см = 260 мм.
3) S = A*B = 15*15 = 225 кв.дм.
4) 500 см = 500:100 = 5 м.
5 га = 5*10 000 = 50 000 кв.м.
A = S:B = 50 000:5 = 10 000 м. = 1 000 000 см
17/42-11/42=6/42=1/7
7/16-9/16=-2/16=-1/8
-1/8+1/7=-7/56+8/56=1/56
4,2/9x+3,5/14=6,11/21
4,2/9х = 6,11/21-3,5/14
4,2/9х = 12,22/42 - 10,5/42
4,2/9х = 1,72/42
1/9х = 1,72/42/4,2
1/9х = 1,72/10
1/9х = 0,172
1/х = 0,172 * 9 = 1,548
х = 1/1,548 = 0,65