Subtract the smaller number ( the young runner 's time ) from the larger number ( the older runner 's time ) , and that 's how many seconds the younger runner should wait before starting .
They both cross the finish at the same time .
Subtract the smaller number ( the young runner 's time ) from the larger number ( the older runner 's time ) , and that 's how many seconds the younger runner should wait before starting so that they both cross the finish at the same time .