An = a1+ d*(n-1)
n-1= (an-a1)/d
n = (an-a1)/d +1
n= (72-6)/2 = 66/2 =33
<span>0.5(x+4)-0.4(x-3)=2.5
0,5х+2-0,4х+1,2=2,5
0,1х+3,2=2,5
0,1х=2,5-3,2
0,1х=-0.7
х=-0,7:0,1
х=-7</span>
5/9+3/4=20/36+27/36=47/36=1,11/36
23/40-3/8=23/40-15/40=8/40=1/5
2/3 * 9/10 = 2 * 9 / 3 * 10 = 3/5
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= 13/5 * 35/26 = 7/2 = 3целых 1/2
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= 7 * 57 /19 = 21