Question

There are $20$ birds in all. An equal number of birds can and cannot swim. Which of the following pair of equations can help us find the number of birds that can and cannot swim?

• A. $20–6=14,14+6=20$
• B. $15+5=20,20–15=5$
• C. $17+3=20,20–3=17$
• D. $20–10=10,10+10=20$

Answer 1

The correct option is D $20–10=10,10+10=20$

Total number of birds$=20$
Since the number of birds that can swim and that cannot swim are equal, on two number frames, we will place $20$ counters first, then remove counters till we have an equal number of crossed and uncrossed counters.


We find that $10$ birds can swim while $10$ birds cannot.
Hence, the subtraction equation framed is $20–10=10$.

Similarly, on two number frames, if we place $10$ counters first and $10$ later, the total counters will be $20$.
Addition equation: $10+10=20$


Hence, option B is correct, and the number of birds that can swim and the birds that cannot swim is $10$.