How can i use benchmarks to estimate 9/10+4/10

Divide. reduce the answer to lowest terms.5 2/3 ÷ 3 1/9

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(10. in the figure, a aabc is drawn tocircumscribe a circle of radius 3 cm ,such thatthe segments bd and dc are respectively oflength 6 cm and 9 cm. find the length ofsides ab and ac.