ICSE Class X Math 2013 Solved Paper

Question : 4

Total: 46

What number must be added to each of the number 6, 15, 20 and 43 to make them proportional?

Solution:

Let the number must be added be x , then the new number =6+x,15+x,20+x,43+ x
∵ These are proportionals.
‌6+x:15+x::20+x:43+x
‌‌‌(6+x)(43+x)=(15+x)(20+x)

‌‌ or ‌258+6x+43x+x2‌ =300+20x+15x+x2
‌‌ or ‌‌49x−35x‌ =300−258
‌‌ or ‌‌14x‌=42
‌‌ or ‌‌x‌=3.

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