yard, how long will it tae them to mow it toghether? (The answer is 120/7 mins but HOW did they get that answer?
2007-06-02 20:47:04 · 5 answers · asked by cookies_rule_91 3 in Science & Mathematics ➔ Mathematics
Jack mows a yard in 30 minutes, so he mows 1/30 of the yard each minute. Likewise Sarah mows 1/40 of the yard in a minute. After t minutes, Jack mows (1/30)t of the yard and Sarah mows (1/40)t. Working together, we want to find how long it takes to mow ONE yard. So the equation is:
(1/30)t + (1/40)t = 1
Solve this for t.
2007-06-02 20:54:14 · answer #1 · answered by Anonymous · 1⤊ 0⤋
After 1 minute Jack has mowed 1/30. After 1 minute Sarah has mowed 1/40. So together after 1 minute they have mowed 1/30+1/40=7/120. It will therefore take 120/7 minutes = 17 1/7 minute to mow together because 7/120 x 120/7 = 1.
2007-06-03 04:10:13 · answer #2 · answered by Anonymous · 0⤊ 0⤋
takes Jack 30mins to mow => 2hrs = 4 yards
takes Sarah 40mins to mow =>2hrs= 3 yards
together
7 yards = 2 hrs
7 yards = 120 min
1 yard - 120/7 min
2007-06-03 06:41:27 · answer #3 · answered by harry m 6 · 0⤊ 0⤋
Let them take x minutes to mow the yard together
Therefore,according to the problem
x/30 +x/40=1 ["1" indicates complete work in all problems of fractions]
=>4x+3x=120 [multiplying both sides by 120]
=>7x=120
=>x=120/7 minutes.
They can do the complete work in 120/7 minutes
2007-06-03 05:00:41 · answer #4 · answered by alpha 7 · 0⤊ 0⤋
Let lawn have area X
In 1 min Jack mows X/30
In 1 min Sarah mows X/40
Total in 1 min = X/30 + X/40 = 70X / 1200
70X/1200<---------> 1 min
X<---------> X / (70X / 1200) mins = 120/7 mins
Will take 120 / 7 minutes
2007-06-03 14:45:15 · answer #5 · answered by Como 7 · 0⤊ 0⤋