High School

Compute each of the following problems mentally:

a. 25% of 60
b. 10% of 78
c. 30% of 15
d. 80% of 710
e. 15% of $40
f. 100% of 57
g. 125% of 40
h. 5% of 64
i. 3.5% of 60

Answer :

Final answer:

The computations for the given percentages of particular numbers were performed using the understanding of what a percentage represents in relation to the whole. By considering 10% and doubling, halving or summing it as necessary, each percentage was calculated.

Explanation:

The following are the computations for each problem:

a.25% of 60 = 15 (since 25% is a quarter of 100%, quarter of 60 is 15)

b. 10% of 78 = 7.8 (since 10% is simply moving the decimal one place to the left)

c. 30% of 15 = 4.5 (30% is like taking three 10%, so if 10% of 15 is 1.5, three times that is 4.5)

d. 80% of 710 = 568 (80% is like taking eight 10%, so if 10% of 710 is 71, eight times that is 568)

e. 15% of $40 = $6 (15% is 10% plus half of 10%; so 10% of 40 is 4 and half of that is 2, totalling 6).

f. 100% of 57 = 57 (since 100% means the whole quantity)

g. 125% of 40 = 50 (Since 125% means the whole quantity and an additional 25%, so 100% of 40 is 40 and 25% of 40 is 10, which sum up to 50)

h. 5% of 64 = 3.2 (5% is half of 10%; if 10% of 64 is 6.4, then half of that is 3.2) i. 3.5% of 60 = 2.1 (3.5% is half of 7%; if 7% of 60 is 4.2, then half of 4.2 is 2.1).

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