Joan likes to watch the birds in her yard. one morning she notices that there are twice as many robins as bluejays. if she counted 21 bluejays and robins in all, how many bluejays did she count

Find the number of bluejays bird and robins birds as joan counted it
=> the number of Robins is twice as bluejay
=> Robins = 2X
=> The number of bluejay is about to know:
=> Bluejay = X
The total number of birds is 21.
=> 2X + X = 21
=>  3x = 21
=> 3x / 3 = 21 / 3
=> x = 7
Thus the number of bluejay is 7
=> Robin = 2(7)
=> Robin = 14
Thus the number of Robin is 14