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The nearest value is 1,000, because 991,026,973 is around 1,000,000,000 ie. cubic of 1,000 Then we evaluate the unit number, ie. 3 1^3=1, unit is 1 2^3=8, unit is 8 3^3=27, unit is 7 ... 7^3=343, unit is 3 8^3=512, unit is 2 9^3=729, unit is 9.. It means that the result have unit = 7 So, the nearest value to 1,000 with unit 7 is 997 Answer : 997

Very hard way to find cube root of a number. I use Binomial Expansion method. It should be (a+b)^3, which is a Binomial Expansion.

The root is just beloww 1000 and must end with a 7 ... the first attempt is bingo: 997.