Correct.
Again I don't think the
answer in these sort of questions is as important as the
process to get it.
The problem can be solved very easily using algebra, but most 10 year olds aren't quite ready for that yet.
Play around with numbers - so much is gained by playing with numbers.
Guess and check is a legitimate problem-solving technique.
Take a guess.
Let's say the number of dead ants for the 4 days is 100, 135, 170, 205 (increase of 35 each time).
Does this add up to 690? No (it adds to 610). Is it close? (sort of.) Is it too big or too small? (Too small) Do I need to increase or decrease the numbers? (increase)
Ok, so now improve your guess:
1. You could try 110, 145, ...etc and repeat the process OR
2. You could realise that 610 is 80 short of 690, so increase each number in your first guess by 80/4 = 20
(Guessing and checking is an important process for children to go through. It improves basic numeracy, before the big step to more abstract algebra. It also precedes a greater appreciation of algebra, when the time comes, as a tool for solving problems more efficiently.)