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Quantitative Reasoning – Abacus rings and numbers!

2014_QNR 19. Rahul used 4 rings on the abacus rod to make numbers. He used only units and tens place rods to make numbrs, hence making the following numbers:
4, 13, 22, 31, 40

2014_QNR 19_1

How many numbers can he make using six rings if he uses only tens and hundreds place?
(1) 10
(2) 7
(3) 6
(4) 5

Ans: 7 numbers are possible:

(H, T) = {(6,0) , (5,1) , (4,2) , (3,3) , (2,4) , (1,5) , (0,6)} . Option (2) 7.

Question for practice:

How many numbers possible if number of rings he uses is 12?

How many even numbers possible if number of rings he uses is 12?

How many remainders possible if each of the possible numbers is divided by 9 (assuming he has 12 rings to use)?

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