book Maths Puzzle Numerical Ability

What is (i)^42.....is it (-1)?

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book Other Question

How much pure acid should be mixed with 2 gallons of a 40% acid solution in order to get a 70% acid solution? Jen works 7 hours a week more than Ben. Jen worked as much in 4 weeks as Ben works in 6 weeks. How many hours does each work per week?