How many integral values of x and y satisfy the equation 5x + 9y = 7, where -500 < x < 500 and -500 < y < 500?

How many integral values of x and y satisfy the equation 5x + 9y = 7, where -500 < x < 500 and -500 < y < 500? Correct Answer 111

Given:

x and y satisfy the equation 5x + 9y = 7

Formula Used:

In A.P. 

Last term(l) = First term(a) + ⋅Common difference(d)

l = a + (n - 1)d

Then n = + 1

Calculation:

We need to find those integer values of x which will give integer values of y when we put them in the equation.

Put x = -1 y = 12/9 (Not an integer)

Put x = -2 y = 17/9 (Not an integer)

Put x = -4 ⇒ y = 3 (Integer)

Put x = -5 y = 22/9 (Not an integer)

Put x = -13 ⇒ y = 8 (Integer)

Put x = -22 ⇒ y = 13 (Integer)

So here we can observe that values of x (starting with -1) with gap of 9 are giving the integer values for y.

So basically, we need to find the all the multiples of 9 between -500 and 500.

AP will be: -495, -486, …, 486, 495.

Number of terms = /9 + 1 = 110 + 1 = 111

∴ 111 integral values of x and y will satisfy the equation 5x + 9y = 7.

Bissoy MCQ

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