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.