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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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