One and a half is 3/2, its reciprocal is 2/3, the sum of the two numbers is 13/6, and 0.26 divided by 13/6 is 3/25.

Solution: let this number be X.

Equation: 7/12x-4.5 =161/2.

The solution is x=36.

That is, the number is 36.

3.7.3÷[ 18.8-(2.3+ 1.9)]= 1/2

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5. The shortest binding is round bottom and cross binding. 48*4+20*4+35=307cm

6.( 1) Calculated unit price: 18÷200=0.09 yuan/gram,1.2÷160 = 0.07 yuan/gram, 0.09 yuan.

So buy160g toothpaste.

(2)r=0.5÷2=0.25？ cm π*0.25？ * 1=0.0625 cm? 0.0625π*48=3π cm？

R=0.6÷2=0.3 cm? 3π÷0.3? π≈33 times