Q4.  What is the least number which when divided by 42, 72 and 84 leaves the remainder 25, 55 and 67 respectively?

Soln:   To find the least number divisible by all the three we will have to find the LCM and the LCM of these three numbers is 2*2*3*6*7 = 504.

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Now the difference 42-25 = 17, 72-55 = 17 and 84-67 = 17. So the number required is 504+17 = 521.