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Of the Three Numbers, the Sum of the First Two is 45; the Sum of the Second and Third is 55 and the Sum of the Third and Thrice the First is 90. The Third Number is?

Computer MCQs Series for PPSC, FPSC – Most Repeated MCQs | Set 4

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Explanation

• Of the three numbers the sum of the first two is 45.
• The sum of the second and third is 55.
• The sum of the third and thrice the first is 90.
• The third number can be figure out in this way.

Let suppose three number are a, b and c.

The sum of a and b (first two) is 45.

a + b = 45  ________ (i)

The sum of b and c (second and third) is 55.

b + c = 55 ________ (ii)

The sum of c and 3a (third and thrice the first) is 90.

c + 3a = 90 ________ (iii)

By solving these three equations simultaneously, we can easily figure out the third number (c = 30).

Third Number = ?

Solution

Let suppose three number are a, b and c.

According to the given conditions

a + b = 45  ________ (i)

b + c = 55 ________ (ii)

c + 3a = 90 ________ (iii)

Subtracting equation (ii) from (i)

a + b – b – c = 45 – 55

a – c = -10 ________ (A)

a – c + c + 3a = -10 + 90

a + 3a = 80

4a = 80

a = 80/4

a = 20

Put a = 20 in equation (iii)

c + 3(20) = 90

c + 60 = 90

c = 90 – 60

c = 30

Conclusion

Of the three numbers the sum of the first two is 45; the sum of the second and third is 55 and the sum of the third and thrice first is 90. The third number is 30.

Computer MCQs Series for PPSC, FPSC – Most Repeated MCQs | Set 6

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