Это легко
<span>3/6</span> ÷ <span>9/34</span> = <span>1·3/2·3</span> ÷ <span>9/34</span> = <span>1/2</span> ÷ 9/34 = <span>12</span> × <span>34/9</span> = <span>1·34/2·9</span> = <span>34/18</span> = <span>17·2/9·2</span> = <span>17/9</span> = <span>8 + 1·9/9</span> = <span>1 целая 8/9</span><span>
</span>98,6*1 целую 8/9
98 <span>6/10</span> × 1 <span>8/9</span> = 98 <span>3·2/5·2</span> × 1 <span>8/9</span> = 98 <span>3/5</span> × 1 <span>8/9</span> = <span>3 + 98·5/5</span> × <span>8 + 1·9/9</span> = <span>493</span> × <span>17/5*9</span> = <span>493·175·9</span> = <span>8381/45</span> = <span>11 + 186·45/45</span> = 186 <span>11/45
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-0,4(y+6,5)=-4/5
-0,4y-2,6=-4/5
-0,4y=-0.8+2,6
-0,4y=1,6
y=1,6:(-0,4)
y=4
27x+x-18x+18=x(27+1-18)+18=10x-18
9*10-18=72
A₁=10
a₄₅=98
S=(a₁+a₄₅):2·90=(10+98):2·45=2430
Допустим в коробке было Х карандашей. Составим по условию задачи уравнение:
(Х+16):2=14
Х+16=14*2
Х+16=28
Х=28-16
Х=12 - количество карандашей, которое было в коробке