How many 4-digit numbers can be formed using the numbers 4, 5, 6 and 7? How many of the 4-digit numbers are less than 7000?
1 answer:
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for example, let's look at the first set
y+3x =5 or y = -3x+ 5
and y = -3x + 2
y = m + b
the slopes are equal, the y-intercepts differ
that means, they're just parallel lines, no solution