Answer: 5.67.
Explanation:
To place the decimal point when computing 1.35•4.2, we can use the fact that 135•42=5,670.
First, we can shift the decimal point one place to the left for each factor, making the problem 1.35 x 4.2 = 0.135 x 42.
Next, we can divide both sides of the equation 135•42=5,670 by 100 to get 1.35 x 42 = 56.7.
Since we shifted the decimal point to the left two places in the first step, we need to shift it back two places in the final answer, giving us 1.35•4.2 = 5.67.
Therefore, the decimal point in the product of 1.35 and 4.2 should be placed after the first digit, giving us a final answer of 5.67.